Sunday, 26 July 2015

Nitrate Removal by Bacteria In Aquatic Systems

Its more complicated than you think!

Nitrate, its one of the big two bad guys in aquatics systems that people don’t want, and seem to struggle with removing.

The terminology out there to describe both its removal, and the modes of action by which it is removed, is so vastly incorrectly used and misunderstood, that no wonder it causes so much confusion, and therefore difficulty for people to achieve effectively.
First of all, removal of nitrate does not only occurs in anoxic zones (oxygen free) in the aquarium, it also occurs as a process of the metabolic production of cell mass (by algae and bacteria) in Oxic (oxygen rich) environments.

It is important to realize the differences between the forms of biological nitrate removal and how they work, in this way you can then choose a nutrient reduction system. And determine what processes will work with one another.

The processes by which the BULK of nitrate is removed in aquatic systems are:

Anaerobic denitrification (in anoxic conditions, a dissimilatory nitrate reduction process)
Aerobic denitrification (in oxic conditions, an assimilatory nitrate reduction process, that will also remove, and requires phosphate for the process to work effectively)
Anammox – Anaerobic Ammonia Oxidation (in anoxic conditions, a dissimilatory ammonia and nitrite reduction process in which nitrate is not produced by way of removing the ammonia and nitrite before it can be converted to nitrate)

Descriptions before we go further:

Oxic – Oxygen rich environmental conditions
Anoxic – Oxygen poor (or absent) environmental conditions
Aerobic – the process in which organisms metabolize their food in the presence of oxygen
Anaerobic – the process in which organisms metabolize their food in the absence of oxygen

Oxic and anoxic describes the environmental conditions
Aerobic and anaerobic describes the process that occurs in these conditions

Carbon Source/fuel – either organic carbon (used by heterotrophic Bacteria) or inorganic carbon (used by autotrophic bacteria), is the primary ingredient in bacterial metabolism and needs to be present for bacterial metabolism to occur
Electron Donor – the ion that receives the electrons and is broken down.
Electron Acceptor – The ion that gives up electrons (Oxygen O2, Nitrate NO3, Sulphur SO4, Carbon Dioxide CO2, etc) and is reduced, in turn oxidizing the electron donor

Anaerobic De-nitrification

In this process, predominantly heterotrophic bacteria, take Organic carbon, nitrate and its preferred waste product to produce an end process of denitrification resulting in di-nitrogen gas.

In this way:
Fuel Source = Organic Carbon (OR inorganic carbon depending on if they are heterotrophs or Autotrophs, but this is the realm of mostly heterotrophic bacteria)
Electron Acceptor = Nitrate NO3
Electron Donor = whatever waste product it is digesting, solid waste, fats, lipids, cellulose, it is widely varied.

More accurately, the organic carbon is liberated from the waste product being assimilated by the bacteria, which they use for the reduction. The breakdown of the waste is a positive by-product of the reaction, and the breakdown of these by products are then processed by other bacteria and so on.

It is adding organic carbon artificially that is ENHANCING this process, and helping to break down excess nitrate, if not enough organic carbon is present.

Here, bacteria take NO3, dissimilating the nitrate, through several steps such as nitric oxide/nitrous oxide for example, to dinitrogen gas, which is then gased off to the atmosphere.

The Nitrate, along with the organic carbon is what they use to process their food source (waste of any description in the anoxic zone they are residing in). The Nitrogen Gas, now liberated from the oxygen in the NO3 molecule, now gases off, eventually, into the atmosphere after it has been dissimilated.

Some of these bacteria can operate as facultative anaerobes, meaning they can function both aerobically and anaerobically. They can be either Heterotrophic bacteria (and therefore benefit from the addition of organic carbon) or Autotrophic bacteria (and use carbonate, bi-carbonates and CO2 as their carbon source), autotrophic denitrifying bacteria however, are not as prolific or as common as heterotrophic bacteria.

Dosing organic carbon into the water WILL help this process if the predominate species of denitrifying bacteria are heterotrophic (weather or not they are obligate aerobes, obligate anaerobes of facultative anaerobes), but generally, there is enough organic carbon released from the breakdown of solid waste (that is their food source) to fuel this process, at least in an aerobic environment.

If they are Autotrophic (which is less common and less prolific) they will use inorganic carbon sources present in the water column, or inorganic carbon sources that are taken from the surrounding environment, either as CO2 or carbonaceous material from calcium carbonate based substrate, as their carbon source.

Because there is such a vast surface area in Aquariums in substrates such as live rock and deep sand beds, or substrate beds of significant depth in freshwater tanks that are commonly applied to promote Biological activity, the amount of waste caught up in these areas, when broken down, liberates enough organic carbon to be able to fuel anaerobic denitrification without adding organic carbon sources, which is usually only added to fuel aerobic assimilatory denitrification.

However, to augment these systems, and promote additional dissimilatory denitrification, additional organic carbon may need to be added into Aquatic systems with limited organic carbon reserves.

Anaerobic denitrifying bacteria will also use suplhur SO3, for their electron acceptor, as is the case with Sulphur based denitrators.

As this process is most often than not reliant on natural organic carbon sinks being liberated through the breakdown of waste, it is obviously a system that needs to mature these reserves of waste in order to fuel nitrate removal long term, and also provide an oxygen free zone to allow fermentation and removal of nitrate.

Aerobic De-nitrification

Aerobic De-nitrification occurs in oxygen rich environments. The bacteria involved are heterotrophic as with anaerobic denitrification, however they do not take in nitrate as their electron acceptor.

In this process, the heterotrophs take Nitrate and phosphate to build cell structure (as part of their metabolism, just like ALL bacteria do), along with organic carbon as a fuel source, oxygen as their electron acceptor and Varied Waste products floating around in the system as their electron donor.

Fuel Source = Organic Carbon
Electron Acceptor = Oxygen
Electron Donor = Varied Waste Products

In this way they build cell mass using the nitrate and phosphate, which then increases the size of the microbial herd in the system. The assimilation of nitrate and phosphate is carried out by all bacteria, it is in this application however, that we take advantage of the extreme growth rate of heterotrophs to remove bulk amounts of N and P.

This is then removed, mostly by a protein skimmer/foam fractionator. Organisms such as sponges and corals and other filter feeding organisms also feed on this Bacterioplankton and it constitutes a large percentage of their food source, both in nature and in tanks running organic carbon driven systems.
In phytoplankton, the ratio of uptake is 106ppm of organic carbon : 16ppm nitrate : 1ppm phosphate. 106:16:1.

In bacteria, it is theorized and has been shown in preliminary studies to be a ratio of around 50ppm organic carbon : 10ppm Nitrate : 1ppm Phosphate

This means that unlike anaerobic denitrification, which uses the pre-exisiting nutrient sinks in the anoxic zones of the tank, Aerobic denitirifcation requires the constant dosing of Organic carbon, and sometimes, in nitrate limited environments, nitrate sources as well. You can read about nitrate limitation here (insert link to blog post here)

This process, is therefore termed an Assimilatory denitrification process, as it assimilates nitrate (and phosphate) into its cell structure as nutrition, rather than dissimilating nitrate to scavenge the oxygen in dissimilatory Anaerobic denitrification.

This process of assimilatory denitrification Is beneficial if you are trying to combat both nitrate and phosphate issues. Sometimes you can become nitrate and/or phosphate limited (such as in the link above) and this can effect the overall systems performance.  

The first reason for this system not working (assimilatory nitrate reduction) is because they are nitrate limited. Being nitrate limited to bacteria is like when we do not have enough iron in our blood to allow the hemoglobin to carry oxygen in our red blood cells.

It is a limiting factor.

The second reason, is that people run GFO, or some other form of nutrient export for phosphate, which effects the redfield ratio and limits the uptake of nitrate.

Trying to run an enhanced nitrate (and phosphate) removal system where you actively dose organic carbon for Assimilatory nitrate reduction, and then use a system that interferes with that system, is bound to fail.

Anammox – Anaerobic Ammonia Oxidiation      

This is a process that is not very much considered.

It is the process in which ammonia (NH4+) is combined with Nitrite (NO2-) by AUTOTROPHIC bacteria (that use inorganic carbon, either carbonates or CO2).

Although several chemical conversions and reduction processes occur within the bacterial cell, the overall conversion representing Anammox is as follows:

NH4+  +  NO2-  =  N2  +  2H2O

Fuel Source = Inorganic Carbon
Electron acceptor = Nitrite
Electron donor = Ammonium

Although this is, in the way of describing it, NOT in fact a denitrification process as we in the Aquatic industry term it (denitrification being the removal of NITRATE) because there is no nitrate actually being removed, it is important as the net result is the same and the process is similar to that of other forms of nitrogen removal.

In this process Nitrous and nitric oxide, and sometimes ammonia (through reduction processes) can be produced during the conversion of ammonia and nitrite to dinitrogen gas and H2O.

Although this usually occurs in the bacterial cell itself, it has been proposed that in systems experiencing high levels of Anammox, that ammonia can in fact spike.

In an aquatic system with livestock, this could potentially be an issue.

HOWEVER, as discussed, the process of anaerobic bacterial metabolism (fermentation) is in fact much slower than ammonia uptake, one reason why you need a large deep sand bed, to provide an oxygen free zone, and also to reach a critical mass to ensure you have enough bacteria to perform anaerobic denitrification.

Uptake of ammonia by aerobic heterotrophs and Autotrophs is much faster. By design we not only want, but also achieve, much larger volumes of oxygen rich surface area in our systems. Any ammonia produced from this process would logically, and in my opinion, be quickly chewed up before a spike actually occurred. And would most likely only occur in localized zones, and not to any noticeable or even detectable levels.

If you were to get a crash of this bacterial population however, through disturbing and introducing oxygen into the anoxic zone, killing any anaerobic bacteria, or by means of toxicity from, for example, supplements or changes in water conditions, the ammonia bound up in the cells could, and more than likely will be released, resulting in mass transfer of ammonia into the system.

The killing of any bacteria creates a Glut of biomass in the system which then proceeds to break down, weather it is annamox bacteria, denitrifying anaerobes or denitrifying aerobes.

This can also happen when an overdose of organic carbon in Aerobic organic carbon driven systems occurs, as there Is not enough oxygen to support the bacterial respiration and bacteria starts to die, releasing the protein into the water column, which then breaks down into ammonia.

My point here is, avoid bacteria die offs, crashes, and just generally, don’t screw up.

Each of these systems has an effect on the other, and every other biological process then has an effect on these systems as nitrate is the final end product of nitrification.

Educating yourself and being aware of ALL denitrifying systems, and their associated bacteria, will allow you to understand how your system works and how what you are adding is impacting your mass removal of nitrate.

Further to this, firstly understanding how your biological system works in general, and how waste moves within, and in and out of your system, will allow you to fundamentally understand just how important you job of farming bacteria actually is.

As always, any questions or comments leave them in the comments section below.

Suffice to say its bloody great to be back, after life got crazy stupid (really really frikken stupid) I've now settled into a new job, got my mojo back, feeling PUMPED, and this is the first of, I hope, many posts that are going to occur regularly.

So thank you for anyone that has taken the time to read this after my extended absence. 

On Another Note......


I have finally found a way you can cook with carp, finally an answer to the scourge of Australian waterways.

Step 1. Catch carp, and dispatch humanly.
Step 2. Soak carp in large tub with water from the river you caught it in, 5% rock salt and a selection of your favorite herbs, for 3 days
Step 3. After day 3, drain water, wrap in canvas or muslin, and take a rock, roughly the size of a grapefruit (preferably also form the same river system, but as long as it is clean it is fine), and weigh down the carp in the pot.
Step 4. Add a can of buttermilk for every liter of water you add to the pot to cover the carp
Step 5. Bring to a slow simmer and boil for 2 and half hours.
Step 6. Remove the rock from the pot, so you can then remove the carp easily.
Step 7. Take the carp, throw it in the bin, and eat the rock.

You’re welcome.

Thursday, 17 July 2014

Are you reading this Blog?

If So....

THANK YOU!!!!!!!!!!!!!!!!!!!!!

The amount of views I have on some of my posts makes writing these posts and answering peoples questions really satisfying.

Since first setting up this Blog, I have added some features to help me keep track of who is reading this blog (gives me some motivation knowing I have subscribers) and allows all you guys reading this blog,  if YOU so choose, to keep up to date with when I post new content.e down the side of the page.

All the features are down the side (for now, unless I change the layout).


I have started a facebook page for this blog, please feel free to go and Like my page and post any questions you like regarding this blog and the content it contains.

Subscribe And follow by email:

If your interested in my ramblings, please feel free to subscribe, you will receive an email every time i post up new content (keep an eye on your junk mail folder as emails like this can sometime get filtered out)

Follow on Google +

Now don't Poo Poo it, its not that bad, change is sometimes good.

If you have a google account, or wish to create one, please feel free to follow me, and if you so choose, add me to your circles, I will do the same.


Please do not hesitate to ask questions, it keep the posts active and the information flowing, post here, and  on the facebook page as well if you wish.

Finally, if you want to link my blog on a forum etc, please go right ahead. If you would like clarification on anything on any of the posts, and would like my input in any threads on these forums, please just post a comment with the link underneath the relevant blog post, and ill be happy to weigh in if you so wish.

Also, if you have any subjects you wish me to write about, i will add them to my growing list of things to post content about.

Thank you to everyone reading this blog. I hope the content I continue to put up is useful.

Saturday, 12 July 2014

Protein skimmer sizing and application - a logic and experienced based approach

Before I begin, I would like to reiterate the purpose of this blog. 1. Because I have not posted in such a long time and 2. Because this subject hits the mark in regards to my mission statement.

This Blog evolved out of a need to provide information that, as far as I can tell, is either incredibly hard to find or digest from information on forums and websites, or simply doesn’t exist all in one place. Or even, simply doesn’t exist.

As such, the subject for this blog post is Protein skimmers, Or Foam Fractionators as they are also called, because there really isn’t a subject that leaves more to interpretation and variance than Protein Skimmers.

I have spent about two months writing, editing, polishing and pulling my hair out over this blog post, so I hope it lives up to my expectations, in your view and opinion.

I have also recently started a facebook page for this blog that you can find on the side bar, go check it out, ask questions etc.

Furthermore, there is NO industry standard In The Aquarium industry for sizing protein skimmers, there is some information that you can base a decision off, but in regards to there being a guide to size a skimmer, you are at the mercy of manufacturers labelling their skimmer as being rated for "x" amount of water volume. And more often than not this can be simply marketing, one reason why store owners in particular need to NOT compare skimmers directly in relation to water volume ratings.

Some brands may have in fact just copied the general design and/or water ratings of other brands (in relation to physical size of the skimmer in relation to height and diameter) and therefore can be taken with less than a grain of salt.

Needless to say, I have come across some skimmers that are so woeful, that all I would personally do with them is fill them with concrete and use them as a door stop, or perhaps an anchor, feel free to use your imagination.

Coming from the aquaculture industry, having sized and applied many commercial sized skimmers in my time, for everything from large aquariums to oceanariums and water treatment systems, I see the need for a standardised system that enables users to size and choose a protein skimmer for aquarium applications.

Might I say at this point, that even the aquaculture industry has some holes in sizing regimes. And a certain amount of experience is needed to develop a working unit with the best results.

My hope is, that one day something like I am about to deliver will be an industry standard, and that skimmer manufacturers will put the relevant information on their skimmers to better allow people to size ANY skimmer for their application, making comparisons between skimmer performance, price, features and component quality easier to make.

As I have not EVER seen anything like this published before (at least not all in one place, or not at all in regards to some of the topics I am about to cover), my hope is that it will be of use to someone, as this is the whole purpose of my blog, to provide information that no-one else has, can, or will provide.

So, to begin...........

A word or two on terminology:

Protein skimmers are also called foam fractionators, weather they were called foam fractionators before they were called protein skimmers or the other way around is something I don't know, I'm not a student of history, in fact I hated the subject.

You will see me use these terms (and variations of the terms depending on what is being described) interchangeably. Floatation may also be thrown in there from time to time depending on my mood. You may just have to deal with it!

Quite possibly no other subject is as confusing and diverse as protein skimmers. The amount of times I have been asked "what protein skimmer do I need for an X x Y x Z sized tank, and the amount of times I have answered "how LONG is a piece of string", is bordering on infinite.

Their vast array of designs, componentry, "special features", and most of all price tag, creates a HUGE amount of confusion. Sometimes with disappointing results and dissatisfaction with the purchase.

There is however a set of "rules" that I stick by, which are expanded on here, to give an overall set of requirements that a skimmer SHOULD meet in an ideal world. These application values suit a broad spectrum of applications and have been formulated as such to give the ability to size Foam Fractionators/Protein Skimmers for any application.

VERY IMPORTANT!!!! every single one of these application factors is either dependant to some extent, or affected ENTIRELY by the others, and taking every one of them into account is of great importance.

I should point out here that in sump skimmers, that use the same pump for both water supply and air flow, CAN NOT control some of these parameters, excelling in some areas whilst lacking in others, for instance having a high water volume turnover and high air volume but low dwell time. These therefore should be governed by these rules to a certain extent, but certain allowances and sacrifices need to made and expected when applying these skimmers as water flow is not, and cannot be independent of air flow in these skimmers, and altering them can be difficult, and impact overall effectiveness of the skimmer. Therefore a good majority of the application factors and values cannot be manipulated, and these skimmers lack the flexibility and effectiveness of skimmers that have separate air flow and water flow pumps.

Therefore, the information below refers MOSTLY to what is referred to as “recirculating skimmers/foam fractionators”, or, skimmers that have a dedicated pump for air flow, and a dedicated pump for water flow.

The application factors and values are as follows:

Factors that DIRECTLY DETERMINE the skimmer performance in regards to design and application and are most important:

  • Dwell time
  • Skimmer turnover rate: Turnovers of the system volume through the skimmer per hour
  •  bubble/air volume
  • Contact rate and mixing (chaos inside the skimmer)
  • Skimmer pass rate (the rate at which the water in the system passes the suction Inlet of the protein skimmer)
  • Height and diameter of the skimmer

Factors that to a certain extent effect skimmer performance, but indirectly, and are not to do with the actual design of the skimmer, but how it is applied and how it interacts with the rest if the filtration system:

  • Product water mixing (how the fractionated water is mixed back into the system water stream
  •  Filtration design (extent of solids removal, type of nutrient export, including biological filtration)
  •  Where the skimmer is placed in the filtration or culture system
  •  Addition or absence of ozone

All of these factors in some way or another directly or indirectly effect each other, and it is how they 
interact with each other and how each is determined and applied in a system that determines the overall effectiveness of the skimmer.

Dwell Time

Dwell time is probably the most important aspect of skimmer design, but so many people get it wrong. Through no fault of their own I might add, it all has to do with the volume of air and how TRUE dwell time is calculated.

Dwell time refers to the time it takes for water inside the protein skimmer to pass from entry to exit. The dwell time is manipulated by altering the flow rate from the feed pump supplying water to skimmer, obviously this means you must use a “recirculating” skimmer, one that has an independent pump for water flow and air flow.

Certain organics and pollutants need different contact times inside a foam fractionator/protein skimmer, in order to be removed.

You may only need a short contact time, or, depending on the nutrient load of your tank, and nature of the waste, you may need a longer contact time.

Things such as bubble volume/mass, flow characteristics inside the skimmer, Chaotic action inside the skimmer (mixing) and skimmer height and diameter are all factors that influence dwell time.

There are three general dwell "times" that the Aquaculture industry uses:

1 minute dwell
1.5 minute dwell
2 minute dwell

1 Minute Dwell Time

This is the dwell time usually chosen for applications where absolute removal and best water quality ISN’T required, for instance in pre-treatment of water being pumped from a water source before it enters a culture system, or a low stock load system that doesn’t require top notch water quality.

In an Aquaculture Application this would include:

  • Pre treatment of incoming water
  •  Low stocking density applications
  • High water volume turnover applications, in either culture or water pre-treatment circumstances (where a bigger skimmer due to physical size or budget is not possible) 
  • Where size and budget simply does not allow for a bigger skimmer to be applied, but where application of a skimmer, even at a lower dwell time, is better than applying no skimmer at all

In an aquarium application, this would encompass the following systems:

  • Fish only (fowlr)
  •  Small coral loads with low feed input
  • Non-photosynthetic coral systems or LPS coral systems with inhabitants that like slightly higher nutrient and suspended solid load.
  • Systems run with the "skimmerless" approach in mind, such as a refugium based system using macro algae and phosphate removal media as the main nutrient export system, and clarifying of water and a little extra polishing of the water is needed to take the tank to the next stage. Possibly even operated on a timer.
  • A beginners skimmer, where cost is a limiting factor and there will most certainly be an upgrade in skimmer in the future.

1.5 Minute Dwell Time:

A good middle of the road application rate that will provide excellent water quality
(when applied in accordance with the other sizing factors below) and most commonly used in circumstances that have medium turnover rates and water volumes to be treated, and medium-high nutrient loadings.

In aquaculture based situations this would include:

  • Fish/invertebrate culture and holding system 
  • Raceway and purging systems  
  • Oceanariums, zoo exhibits 
  • Anything with a moderately high nutrient load that requires large amounts of clarification and suspended solids removal.

In aquarium based applications this would include:

  • Most reef systems with moderate feeding and nutrient load  
  • Fish only systems (fowlr) with high fish loads and feed inputs  
  • Berlin systems (relying on the surface area of the live rock to provide the majority of the filtration) Bacterial driven systems requiring removal of nutrient through export of bacterial biomass 
  • Systems lacking adequate pre-filtration, that suffer from high suspended solids loading 
  • Systems applying ozone through the protein skimmer 
  • Mixed reef systems that include SPS corals requiring good water quality, but where that FLAGSHIP top end is out of reach in price range.

2 Minute Dwell Time and Above:

This is the dwell time and treatment rate used where the absolute best water quality is required. It will result in removal of the maximum amount of suspended solids, proteins and bacteria, and is the option chosen when the absolute best water quality is required.

It is most often applied also, where the skimmer is being used to apply ozone, in conjunction with excellent skimming in high nutrient load systems.

In aquaculture applications this would include:

  • Larvae, fingerling and brood stock systems where the absolute best water quality is required for accelerated growth or conditioning for spawning.
  • High load, high feed culture systems, that might perhaps be lacking in solids removal, or have a high nutrient and suspended solids loading that is impacting growth rates or oxygen consumption.
  • Water treatment systems, where maximum removal of suspended particles and nutrients contributing to high BOD (biological oxygen demand) is required to recycle water, or treat water before going into a culture system.
  • Where ozone is being applied (with oxygen input) to remove particles that are hydrophilic, that require oxidation and high dwell and contact times to be removed more effectively by a protein skimmer. This occurs by micro flocculation, by “binding” together particles that are both hydrophobic (easily removed by skimming, they hate water) and hydrophilic (wanting to stay in suspension and remain dissolved in water) particles, removing both more easily. Oxidation of these hydrophilic particles may also render them partially of completely hydrophilic, allowing them to be directly removed more easily also. This would also result in decent oxygen diffusion to increase DO (dissolved oxygen) levels.
  • In regards to the above, where a single unit needs to the job of an oxygen reactor, ozone reactor, and protein skimmer, but the Budget is not available to apply all three. Although not as efficient as applying separate units, it would result in acceptable ozone and/or oxygen transfer and get the required result in a good percentage of applications.  (oxygen and ozone reactors are usually the same unit, except in applications where oxygen demand is larger than the ozone requirement, in this case a separate ozone reactor is applied)

In Aquarium Applications this would include:

  • SPS systems, or systems with delicate corals requiring the best water quality.
  • High food, low nutrient systems, or commonly termed ULNS or ultra low nutrient systems, where nutrient removal in the form of nitrate and phosphate to very low levels is required to promote the enhanced colouration of corals, and therefore, because of low nutrient levels, the corals require large amounts of supplemental food to substitute for the energy lost that the corals gain through photosynthesis and natural prey capture.
  • Breeding systems
  • Coral propagation systems 
  • Large systems with large volumes and surface areas, requiring enhanced removal "per pass" of the protein skimmer, to ensure maximum removal to avoid settling in the system, In the live rock and pockets of the tank that are hard to clean.
  • Large systems often have a hard time achieving adequate flow within the aquarium and often suffer from suspended solids settling in low flow areas of the tank, therefore a skimmer processing large volumes of water, with a high removal rate is ideal  
  • Where space is not an issue!!!!!!!

This is essentially an "in a perfect world" application (in regards to dwell time), where cost isn't a huge 
determining factor and the system requires nothing less than the best.

Skimmer turnover rate - Turnovers of the system through the skimmer per hour

This refers to the amount of times the whole system volume goes through the protein skimmer per hour.

It is usually based on the ENTIRE water volume contained in the system, but in some cases would only be based on a portion of the system volume, for instance, only the tank volume because the sump volume is intentionally oversized, or only the tank volume or tank and sump volume because the system incorporates water storage to intentionally increase the water volume to aid with stability of water parameters.

But, for all intents and purposes, let's say that in most cases, the water volume being referred to is the water volume of the tank AND sump , and consider the sump to be sized accurately and not oversized for the application.

Of course in the real world each system would be approached on a case by case basis.

Again, as there is with a good percentage of these parameters, there is a number of different application rates that you can use depending on your situation. Generally, these being:

1 turnover of the system volume per hour
2 turnovers of the system volume per hour
3 turnovers of the system volume per hour

NOTE: Pre-treatment of incoming water is ruled out here as this parameter is dependent on a closed system.

1 Turnover Of the system volume per hour:

Aquaculture applications:

  • In culture systems (including larval, fingerling, grow out and broodstock) where other filtration components are sized correctly and handling the load well and thorough mixing back into the culture stream water returning to the tanks is being achieved
  • In culture systems (including larval, fingerling, grow out and broodstock) where there is a large volume of water to treat, and higher turnover rates would result in higher running costs or capital costs due to the size of the skimmer going up exponentially as the turnover rate through the skimmer goes up (the same as increasing dwell time)
  • In culture systems (including larval, fingerling, grow out and broodstock) where all filtration has been achieved prior and the skimmers load has been reduced significantly

Aquarium applications:

  • Systems with corals that require levels of suspended solids to feed (non Photosynthetic Systems, LPS dominated Systems
  • Low load Fish only systems
  • Low food input coral systems

1 turnover of the system volume through the skimmer per hour is an excellent starting point and generally the "default" application chosen if all other filtration is keeping up and all other application factors are sized correctly according to the application the skimmer is being applied in. 

In high load systems you may encounter the need for more cleaning or wet skimming to remove more waste.

2 Turnovers of the system Volume Per hour:

Aquaculture applications:

  • In culture systems (including larval, fingerling, grow out and broodstock) where filtration, especially solids removal, is lacking, or load needs to be eased on filtration components removing solid waste.
  • In culture systems (including larval, fingerling, grow out and broodstock) where mixing of the product water is less than optimal (returning to the sump for treated water to be picked up again, instead of treated water being mixed back into the water stream going back to the culture system and the skimmer only drawing untreated water)
  • In culture systems  (including larval, fingerling, grow out and broodstock) where there is a need for ozone treatment without the ability or necessity for a separate ozone reactor. (and also when supplemental oxygen input through the addition of ozone is an advantage to the culture system without the need for high levels of oxygen to be added through a reactor
  • Systems with medium-high flow sumps, resulting in the need for extra treatment passes to capture suspended solids.
  • In holding systems (purging, live seafood holding, quarantine) where shock loading occurs, but other filtration is sized correctly and only moderate loads per cubic meter of water 30-40kgs/m3) are being added.

Aquarium applications:

  • moderately fed tanks with medium fish load and medium to high coral loads.
  • aquarium’s that may have filtration lacking
  • Systems that have supplemental ozone being added via the protein skimmer.
  • Medium to high food input systems operating an organic carbon driven nutrient export system

2 turnovers per hour is a good level to go with if you have a moderately loaded system, or your skimmer just isn't quite handling the load, and you have calculated your turnover through the current protein skimmer is less than this.

This is more than optimal for systems with well designed filtration and waste removal systems, and would result in the system being able to handle more load, especially with the use of Ozone.

3 turnovers of the system volume per hour:

Aquaculture applications:

  • High load systems, all systems with high feed and waste inputs and systems with high stocking densities.
  • Systems that are shock loaded with heavy stocking densities (purging and holding systems with shock loaded densities of 50kgs/m3 and above)
  • Systems that suffer from high suspended solids and nutrient loads
  • Systems that require aggressive solids and waste removal to ease the load on other filtration components
  • Systems that have underperforming filtration components
  • Systems that want to improve their carrying capacity and stocking density or food input per day (very successful when applied with ozone)
  • Broodstock holding systems
  • Larval and fingerling holding systems where increased growth rates are needed by way of improving water quality
  • Systems with partial or complete flow through water supply that requires complete skimming  (no skimming on water supply) or supplemental skimming ( such as when heavy feeding in the tank occurs, and flow through flow rates are low and water quality is suffering from not enough flushing occurring) or both.
  • Systems with a high turnover through the sump

Aquarium applications:

  • High feed systems
  • Heavily stocked fish only systems
  • Systems with requirement for high nutrient removal to maintain low nutrient levels (SPS systems)
  • Heavily stocked and fed tanks utilising organic carbon driven nutrient removal
  • Multiple tank systems with centralised filtration systems
  • Large, deep tanks, where light penetration is of upmost importance and coral growth in the lower levels of the tank is being effected by the clarity of water
  • Systems applying ozone
  • Systems with high-very high flow sumps
  • Large systems over 2000-3000 litres
  • Systems suffering from neglect (if buying an upgrade for an existing skimmer) or if applying a skimmer to systems that have not had a skimmer installed, that are suffering from nutrient saturation problems or solids loading.

This is the application rate to use if the water quality is lacking severely OR alternatively where the best water quality is needed.

Systems with high feed inputs, filtration components that are struggling, systems with a requirement for low suspended solids and nutrient levels (shellfish systems, coral systems, quarantine systems), systems where the design of the filtration and water distribution systems overall are less than desirable or simply systems that need the absolute BEST water quality would apply a skimmer at this treatment rate.

Air/Bubble Volume

Fairly self explanatory, and you would think, this is easy, just apply as much air as possible.

WRONG, buuuuzzzztttt, errhhhhhhh.

So where to start explaining this- well let's start with….   

When you don't have ENOUGH air:

When you don't have enough air in the water mix inside your protein skimmer, you will have to compensate.

Less air bubbles means less chance of organics coming in contact with them, which means you need more time for the air bubbles to contact them for the same water volume.

This means you will need

  • a bigger skimmer (with same ratio of water to air) to allow a larger dwell time as more chance of the bubbles contacting the organics, alternatively, a smaller input pump which would result in a drop in system turnovers per hour, which could effect water quality
  • better mixing inside the skimmer to ensure bombardment rate is higher to compensate for lower air volume

Essentially EVERYTHING needs to be bigger to compensate. If you had X skimmer with everything sized correctly, and you then halved the air volume, everything would need to be twice it's value to compensate.

What happens when you have too much air:

Too much air can result in a few things, and you don't always get these problems, and sometimes they are not visible, but they are more than likely there.

Too much entrained water:

This refers to the amount of water an air plume can carry. When air bubbles, especially fine air bubbles are put into a water column, as they rise they take water with them.

This is the exact purpose of an airlift, and is why aeration systems in large water courses, lakes, ponds etc, that utilize bottom diffused air are much more effective at moving large volumes of water and creating better circulation than aeration on the surface of the water (paddle wheels and other floating aeration devices that do not utilise diffused air)

This means that the skimmer can be difficult to adjust, and can take too much water with with the air plume (essentially this results in more water in the skimmate in relation to the energy put into the skimmer to make that air, which means more skimmate needs to be produced to get the same amount of organics out, which means you use more energy to do it.

I hear the aquarium nerds (and I use the term affectionately as I am one) saying that sometimes you want to wet skim.

Yes that is true and I totally agree, but what if you also want to dry skim?

If your skimmate at "dry skim" in a skimmer that has too much air, and therefore a higher volume of water entrained in it, has a percentage of water at (pulling numbers out of thin air here) 27%, and your aiming for a wet skim with 35% water in it then that's fine, as you can simply raise the foam head in the skimmer.

But what if you want a drier skim, with for instance 10% water in it, you could I suppose clamp the air intake line on the protein skimmer, but how would you know how much air in going in?

I suppose you could then buy an air flow meter for the air suction line. But then you have to recalculate dwell time, turnover rate, bombardment rate etc as the air volume is less, this will mean you will have compensate to achieve the same effectiveness.

Having said this, a Skimmer with TOO MUCH air, can have its air input reduced, the dwell time in regards to water volume will therefore simply have to be recalculated. There are several things that need to be taken into account, but its doable.

As the air volume inside the skimmer is part of the overall volume inside the skimmer, and the air reduces the water volume inside the skimmer, this air volume therefore needs to be added onto the skimmer vessel volume after dwell time is determined in order to achieve an accurate dwell time as the air volume will be a volumetric percentage of the matter inside the skimmer.

If it displacing 20% of the water, then that's 20% less volume of water inside the skimmer chamber and dwell time gets thrown way out. If you then go altering that volume EVERYTHING needs to be recalculated.

General rule of thumb, understand how much sir is too little and how much air is too much (for your given application in relation to dwell time and skimmer design) and choose a skimmer meeting these requirements.

If in the event you have too much air, you can alter the air volume to achieve the right air:water ratio, AND the right dwell time for your application.

SLUG flow:

Pretty simple this one, too much air and not enough proper mixing results in the air bubbles forming together and creating a slug of air (a larger air bubble), this races up through the column and disturbs the foam head, reducing efficiency. It's also a waste of energy in producing the air as the air that forms together and creates slug flow is then useless for skimming and was, in the end, pointless to produce as it achieves nothing.

Micro bubbles out of the outlet:

Too much air can sometimes result in the air flowing out the outlet pipe of the skimmer causing micro bubbles in the sump or even worse, in the aquarium, but is not so much an issue for aquaculture systems.

This is however, especially a problem when things like biopellets are added (organic carbon sources in general can cause this periodically when too much organic carbon is present in the water), new filter pads and amino acid supplements can also cause microbubbles to escape into the display as the products in these materials (mainly hydrocarbons and other surfactants, as is the case with amino acids) are changing the surface tension of the bubble, making them harder to pop and meaning that they stay in suspension longer.
The right amount of air, compared to having potentially too much air, can cause this to happen more readily. But is only usually an issue when there is TOO MUCH of a certain hydrocarbon present. But, even in small amounts, in a skimmer with too much air (and therefore a higher percentage in relation to the water volume), it is more likely to happen as there is physically more air that is potentially able to exit the skimmer.

The ideal amount of air inside a protein skimmer falls somewhere between 20%-40%, and sometime a little more depending on dwell time (as dwell time goes up, flow rates through the skimmer reduce and the % of air inside the skimmer increases as the air suction volume stays the same, therefore, mixing and distribution of water and bubbles becomes even more important as air volume percentages rise.
The beauty is, if you have a skimmer creating slug flow, and has potentially too much air, you can alter it with a ball valve, the exact volume of air for a given skimmer will depend on the individual skimmer, and is a function of its dwell time in its particular application, but the above is a good guideline.

The right amount of air is crucial to a properly designed protein skimmer. And before I get all the aquarium hobbiests up in arms saying "my skimmer has more than 50% air volume and my tank is very clean etc etc etc etc" let me say this.

Just because something works well, doesn't mean it can't work BETTER.

Too much of (potentially) a good thing like air volume inside a protein skimmer, can be infact a bad thing.

I am NOT saying that Higher air volumes than 40% are going to be detrimental, I am simply saying that the chance of slug flow and other negative issues can be increased as air volume goes up. And in fact, there may not be ANY benefit in adding more air. Each skimmer will be different, and at the very least if you have too much air you can adjust the sir suction with a ball valve on the venturi line to find the sweet spot.

You must also remember that if you air volume inside the skimmer goes from 20% up to 40%, you reduce the amount of water in the skimmer, this then throws out dwell time, which means, you need a bigger skimmer to achieve the dwell time you are aiming for, this means a bigger air input pump (as a larger volume reaction chamber will mean to reach the same air % inside the skimmer you will need a bigger pump to produce more air) and more room is needed to house the skimmer as the skimmer is physically larger.

Contact rate and mixing (chaos inside the skimmer):

This is a little harder to quantify as there are no real ways to measure this.

Essentially it is the way the water inside the protein skimmer is mixed and then distributed throughout the skimmer.

Good mixing means the waste particles come into contact with more bubbles (theoretically) and upward motion through the skimmer results (theoretically) in the waste particles having less of a chance of being swept towards the outlet of the skimmer and back into the system before being removed.

This really just comes down to good internal design and sometimes, the use of nozzles or directional flow inlets and/or baffles to ensure the water (and air) first goes up, and then down towards the outlet. Counter current (flowing the water down through the air column whilst bubbles flow up) is still recommended in most cases, but other forms of internal mixing can achieve the required results as well, and further enhance this design aspect.

Essentially what im getting at is, don’t use a skimmer that has a water inlet at a point in the skimmer where there Is a  potential for a percentage of that water to flow, in some degree, straight out of the skimmer before being treated.

This may seem very trivial, but if good mixing and internal design results in a skimmer pulling out 10-20% more waste, or more, because the increase in efficiency and internal mixing results in waste being contacted by more bubbles, then the placement of the inlet in a skimmer can be seen as being incredibly important.

For instance, you have two skimmers of the same brand, and same design, except that the placement of the water inlet is higher in one than the other, both with a 30 watt pump churning out 1500lph of air. That simple bit of plastic directing flow inside the skimmer that you thought was useless, may just possibly mean that one of the pumps pulling that same 30 watts, is now resulting  in the skimmer being 20% more efficient. It means you potentially need to use less nutrient control media as the percentage of suspended solids being exported is higher, it means an increase in water clarity, it means better water quality.

It also means that you need to look for a skimmer that is offering good mixing, and use your common sense and best judgement to see how the internal mixing is resulting in a better contact rate. Be careful, some skimmer manufacturers will put intricate internal designs into their skimmers which at the end of the day don't do much, and sometimes impede flow, or make it worse!

Also look for ease of cleaning at this point, vinegar can only get you so far, you'll thank me, I assure you. Make sure that you chose a skimmer that can be pulled apart and serviced easily.

Skimmer pass rate (the rate at which the water in the system passes the suction Inlet of the protein skimmer):

The amount of times the water is passing the skimmer water suction inlet is a HUGE influence on how well it will perform.

For an example, you have 2 identical skimmers

Each skimmer is achieving a 2 minute dwell time, with 1 system turnover through it per hour.

If you have one of those skimmers placed on a system that has a 5 times per hour turnover rate through the sump/filtration system, you may find it is pulling out (picking a number from thin air) 1 litre of skimmate a day.

Exactly the same skimmer, that has a 10 times per hour turnover rate through the sump/filtration, has water flowing past it's inlet twice as fast. This means that to process this waste at the same speed, theoretically you need to have a skimmer capable of processing twice that of the 1st skimmer.

The velocity of the water flowing past the skimmer suction inlet could mean that waste is not pulled into the skimmer as effectively, depending on the nature of the sump design it could redirect water along a different path at higher velocities, meaning some particles may get swept that way, instead of past the skimmer inlet.

It could also mean, depending on the nature of the waste particle, that it could force the particles up, or down, eluding the suction of the skimmer inlet.

The first skimmer, in simple terms, is applied in a system, taking water from a sump, that is spending TWICE as long in the water in the vicinity of the skimmer suction inlet.

It is important to take this into account when sizing a skimmer, and make sure that you compensate for this in your system turnovers per hour through the skimmer, and your dwell time.

A good ratio to work from is a system volume turnover rate through the skimmer: skimmer pass rate of 1:3.

Where did I come up with this number?


Generally any filtration system that is sized and designed as a modular filtration system, is sized on the filtration units being able to handle up to 1/3 of the flow (in an aquatic system aiming to achieve a turnover rate of 3 times per hour in order to maintain water quality).

Mechanical filtration is obviously ruled out of this as all water needs to passed through mechanical filtration in order to be clean enough to pass onto and through subsequent filtration systems.

Having said this, that isn't to say that more is not better, but most of the time the water flow rates and hydraulic loading of the individual filtration units only requires a portion of the flow rate of the system. And therefore the overall water flow can be split and treated by several filtration units simultaneously, and then mixed and merged into one stream for distribution back to the tanks. Usually via gravity.

In an aquarium application, the filtration is most often (unless it is an incredibly large system utilising a centralised filtration system allowing gravity feed back to the tanks) running on circuits in and out of the sump, with a pump returning the water back to the tank.

A turnover rate(through the skimmer) : skimmer pass rate ratio of 1:3, is the same as a treatment rate of 33% of the system volume by a skimmer in a system turning over its volume 3 times per hour.

As I said though, it doesn't mean higher ratios cannot be used effectively. Lower ratios closer to being equal (1:1) and even lower (1 : 0.5), would obviously result in better water quality, as the water would be passing through the skimmer FASTER than it is passing through the filtration that it is drawing water from, resulting in higher processing rates.

So for instance, if this is the only parameter being taken into account (which it shouldn't be, see above in turnovers per hour) then you need 1 turnover through the skimmer for every 3 system passes through the filtration system (past the skimmer suction inlet).

If you have a 10 times per hour turnover rate through the filtration system, then you need 3.3 system turnovers through the skimmer. MINIMUM.

If your previous parameters such as nutrient loading, solids loading, influence by other filtration and requirement for water quality have dictated that this has already been met, or is higher (as in a higher turner through the skimmer than 1/3rd that of the system turnovers), then your golden.

If it is lower there are two things you need to do

1. Either increase the system turnover treatment rate through the skimmer OR
2. Make a decision that the other factors you have chosen (dwell time for instance) have compensated enough and a drop in the ratio is acceptable.

Higher or lower ratios may be needed, the purpose of this information is to give you the information to make an informed decision.

Please also see the system turnover treatment rate section for information on different applications that skimmers are applied into, (running straight off tanks, in sumps).

Hang on the back skimmers (skimmers that hang on the back of tanks) could be influenced by this as flows in display tanks themselves are usually very high, and is something you will want to take into account when choosing one.

Height and diameter of the skimmer:

This goes hand in hand with contact rate and mixing, and will either enhance or hinder the chaos rate Inside the skimmer, the internal design will also directly effect this.


Height in a skimmer achieves many things and even when the skimmer is skinny and tall, it will generally result in a slightly better skim.

The height allows introduction of the water from both the skimmer inlet, and the pump delivering the air, to be introduced further away from the outlet and from one another, meaning a longer contact rate, better mixing and less chance of untreated water making it to the outlet without being treated.

Water that does make it to the bottom, if the skimmer is designed this way, can be picked up by the air generating pump and delivered back into the Center of the column, Improving mixing and adding to the chaos intensity inside the skimmer.

It usually also means that the upper column is calmer, allowing the bubbles the rise and form a stable foam head, resulting in a more stable and constant skimmate being produced.

If the skimmer is short and squat? Well all of the above is essentially reduced, and other aspects may need to be redesigned in order to compensate.


In a tall skimmer, you may not necessarily need a bigger diameter unless height is a restriction or to get volume, in which case you would need to go out, and not up.

In most cases the maximum height of a skimmer is going to be about 2.5 meters, which is bloody tall, but usually even these will have auto wash downs on them to make cleaning easier. But even so, any higher than this and maintenance, when it does need to be done, will be a problem. And not just a problem but a nightmare, ever looked into the body of even a small skimmer in a moderately loaded system, that hasn’t been cleaned for 2 months? Not a pretty sight.

Not to mention that the height you have to actually house it in the first place may determine whether or not you need to increase the diameter to increase volume. Most manufacturers of large skimmers will take standard room heights into account when designing their protein skimmers of both normal residential and commercial buildings, but obviously this can only get you so far.

In aquarium applications, where maximum heights inside most cabinets are 700-1000mm at most, the diameter will need to be increased in order to manipulate volume to achieve the desired dwell time and turnover rate through the skimmer that you are aiming for.

An increased diameter in these sorts of applications, producing a shorter skimmer with a larger diameter will have an increased D:H ratio. Although diameter will not usually exceed height in this ratio, sometimes it can.

So what does this mean, well, it means one very important thing over all others. It means you need Really, REALLY good mixing. Multiple pumps delivering the air/water mixture may need to be used around the circumference of the skimmer in order to deliver an even amount of air (and water) for the larger cross sectional area.

Along with this comes directing the flow in certain ways (creating circular currents etc within the skimmer) or utilising mixing nozzles in the skimmer and/or plumbing arrangements outside the skimmer (before the water enters the skimmer body) to improve mixing.

This is where the design of the top of the skimmer (the neck and upper area where the foam head forms), and how the water is mixed in the chamber comes into play.

The need to achieve a balance between huge amounts of chaotic movement inside the skimmer, and a calm stable foam head in the upper portions of the skimmer is now needed. There are a few ways to do this, one is putting the air into a separate chamber to mix first inside the skimmer that is then distributed throughout the skimmer, this is most often seen as a diffuser plate inside the skimmer, but this reduces greatly the amount of chaotic movement inside the skimmer body reducing efficiency as it only directs water upwards, in a single stream, not exactly well mixed in THE BODY OF THE SKIMMER in my opinion, although it may be mixed well under the diffuser plate.

The chance of slug flow is also increased with a diffuser plate as the air mass in being concentrated into a much smaller area, and air bubbles can join up under the diffuser plate as well, compounding the issue further.

The other way that calming and stabilizing the foam head is often achieved is by slowly tapering the neck, or even making the whole skimmer a coned shape, in order ease the bubbles upwards and concentrate them to a certain degree without having the air bubbles and water suddenly have to change direction and be suddenly concentrated into a small riser tube.

Multiple pumps can also be used, but this can increase footprint, albeit ultimately providing redundancy. With smart design both in the delivery plumbing and the internal design and mixing, one pump can be used in a skimmer with a larger diameter to save room.

The use of wider riser tubes (of over 3 inches) is becoming more popular now as well, which to a certain extent helps this, but is more because of the huge amounts of air skimmer manufacturers are putting into skimmers these days, concentrating such a huge percentage of air into a riser neck smaller then 3 inches is asking for trouble with overflows, not to mention balancing and tuning would be an absolute nightmare.

In overly wide skimmers the majority of the volume NEEDS to be utilised, as the width is compensating for height to increase the volume in order to manipulate dwell time and allow higher flow rates to accommodate larger turnover rates through the skimmer.

It is because of this that most overly wide skimmers that aren't particularly tall (most aquarium skimmers) and even large commercial grade skimmers that have a maximum height they can go to (not only for workplace safety and ease of operation but also because of shipping) incorporate a bottom manifold, baffle or box over or connected to the gravity outlet of the skimmer, so that the water has no other way than to be drawn from the absolute lowest place inside the skimmer. This allows larger diameters to be used, without getting bubbles in the outlet water and ending up in the system causing turbidity.

IN A PERFECT WORLD (where everything is magical Christmas land)

Ideally a skimmer should be as high as possible, with a good cross sectional area ( to allow good mixing)  but not be overly wide.

I could throw out ratios here and say it could be between this ratio being ideal, and that ratio being not ideal but could be used with attention to good internal design and good mixing. But because there are so many variables as discussed above it is hard to quantify what ratio actually works best, because with careful design in regards to mixing and layout, almost any height : diameter ratio can be used within reason.

My advice in this instance, use this information to solidify your decision based on common sense. That and go with a reputable and trusted skimmer manufacturer.

INDIRECT factors that affect skimmer performance (system design and functionality)

Product water mixing (how the fractionated water is mixed back into the product water stream returning to the tank):

Designed and applied correctly to remove the maximum amount of solids per pass, water should be directed downstream, away from the suction inlet of the skimmer.

In the situation where a skimmer is sized below the optimum, this is even more important.

Why would you want to skim the water twice? Picking up a percentage of already skimmed water (or semi skimmed water, with a skimmer not sized at optimum) as opposed to water that is completely untreated?

In the early days I use to think that double skimming/processing was a good move too, many MANY years ago......... when I was an idiot.

If you are picking up already fractionated and processed water, then there is a percentage of water coming from the culture tank that you are missing out on skimming that is laden with organics and particles requiring removal.

I hear the people say well if the skimmer is under efficient wouldn't this be good as you picking up any waste that hasn't been skimmed out on the first pass?

In this case the proposal is to skim a percentage of partially under skimmed water along with some COMPLETELY unskimmed water, instead of treating 100% unskimmed water, leaving an even higher percentage of completely under skimmed water, underskimmed? creating even more (and progressively worsening percentages of) partially underskimmed water along with MORE COMPLETELY underskimmed water UNDERSKIMMED?


In fact, I cannot physically make a big enough fart noise with my mouth to express how erroneous and just plain wrong this approach is.

Direct the water downstream, you'll be picking up 100% unskimmed water every time that is coming straight from the display tank.

In the event that the skimmer is run off of the side of the culture tank (in large aquaculture systems for instance) weather it be one tank or multiple tanks connected to one system, then steps should be taken to mix the water into the product stream so that it is evenly distributed and distributed AWAY from the pickup of the suction inlet of the skimmer.

Filtration design (extent of solids removal, type of nutrient export, including biological filtration)

Filtration design plays a big part in what skimmer you choose, and the applications you use to determine the size of that skimmer. Each phase in the filtration process, along with where each filtration unit is situated In relation to the skimmer will effect it's performance and require that the skimmer be sized accordingly.

Solids filtration

Solids filtration can be anything from gravity separation (swirl separators, radial flow filters, baffles) to course filtration (open cell sponge, yep that ridiculous black coloured crap we all hate cleaning out, which is ironically great as a biological media), screen filters (like parabolic screens, and drum filters), to fines filtration like (bead filters, drum filters utilising finer screens, sand filters, pleated filters and fine matt).

Usually a mechanical filtration system will use more than one stage to ease the loading on the next and so forth.

In this application, if solids were being removed by gravity separation (baffles, swirl separator, filter bags, all of which generally filter solids of around 200 microns and above) and then a fines filter (fine Matt, drum filter, sand filters, which remove particles 10-200 microns or more if course solids removal is not used) then the skimmer would not need as high of a dwell time and would not need to process as many system volumes per hour as the loading on the skimmer is lower.

If however the system only employed filtration to remove larger particles, like a low tech system using only gravity separation, then the skimmer would have a huge increase in load on it, and therefore dwell Time and system turnovers per hour through the skimmer would need to be higher in order compensate for this, and to remove larger quantities of solids to improve water quality.

In some cases skimmers are used AS the fines filtration system, passing all of the water through them, and therefore would need to not only handle a much larger volume of water (the entire turnover flow of the system) but also a higher solids loading.

In an aquarium application, usually the solids loading and nutrient loading is higher, and higher quality water is most of the time required, and so as a general rule, dwell time should be higher and so should turnover rates through the skimmer.

Placement of the skimmer in the filtration or culture system:

The Above talks about an application where the skimmer could be used a solids filtration device in itself to remove fines.

But what if it is handling cleaner water (after solids have been completely removed from the system as much as possible) or filtering water from other filtration devices (like bio filters, UV sterilisers) then what is the impact of this on the skimmer?

What would be the impact of placing the skimmer directly on the culture tank? With no pre-filtration at all?

Firstly, in either of these applications, weather in an aquarium or an aquaculture system, you must consider what the implications will be from placing fractionated water into a treatment stream that is then possibly being used by other filtration processes.

If using ozone, it should almost always be placed downstream of any biological based filtration, bio filters, biopellet reactors, degassing units, denitrators, refugiums, cryptic zones, anything that could possibly be effected by residual ozone.

Although good mixing of product water will usually negate this, and in a high load system most ozone will be chewed up almost immediately, it is something you must definitely consider.

In terms of a skimmer not applying ozone, there are two things you need to consider.

1. Will the filtration work better if skimmed prior (eg:static biological filtration), or in fact require the water to be skimmed in order to work better (in the case of poor solids removal)
2. Will the skimmer impact the result of that filtration in a positive or negative way if skimmed afterwards.


In the case of situation 1 (which overlaps situation 2) in most aquarium applications and even in some Aquaculture applications, the skimmer may need to be applied after the solids filtration and before the biological filtration to stop the bio media from clogging. It would most definitely be necessary to treat prior to any chemical filtration or reactors (phosphate removal, ozone reactor) to not only remove any possible nutrient to ease the loading on chemical media, but also to ease solids loading on them.

In regards to skimming prior to biological filtration, both the removal of waste, and increase in both ORP (even when not using ozone) and oxygen levels will result in better nitrification.

There is also an argument, and a very solid one in fact, that skimming before returning it to the tank via a polishing filter (pleated cartridge, sand filter, bead filter, any other fines filter running lower micron filtration) will also ease the load on that filter, AS WELL AS increasing the DO levels of the system water before it is sent back to the tanks.

So the answer to number 1, is an unequivocally solid YES.


Positive and negative impacts of applying a skimmer after other filtration

Postive impacts:

Solids removal; especially the removal of fines that clog biological filtration media and settle into the filtration system causing nutrient sinks and mulm deposits. This is most often seen in low tech aquaculture systems using primarily gravity separation as solids removal, and I'm going to say a good majority of aquarium systems. As filter socks gain an ever increasing momentum in reef and marine aquarium systems, the need for finer filtration is needed. At the most, filter socks will generally filter down to 100micron, (with most being 200 micron) and although they will trap smaller particles once they start to clog, clogging is something that, in the end, is not something we really want, nor can you rely on it to produce better solids removal.

Protein skimmers will filter particles from 50 microns to 1-5 microns (depending on dwell time and the addition or absence of ozone) and so in this case, definitely a plus where solids removal by other means is lacking.

In the case of Nutrient removal by means of an organic carbon driven system:

Especially when using an organic carbon driven system based on biopellets, the skimmer should be placed after the biopellet reactor. If possible with the biopellet reactor feeding directly Into it.
In liquid organic carbon systems, this doesn't really matter, but could be placed before the biological media, to reduce biofilm buildup, if of course you are not using ozone, which could negatively impact your nitrification.

Skimming as a means of removing particles that have been oxidized:

If using an ozone reactor, you want the water that has been treated with ozone to then be skimmed by the skimmer, as the particles will be easier to remove (more on this in the next section)


Nutrient removal by means of a refugium of phosphate reactor (or both):

It is important in this instance to place the skimmer before the refugium and phosphate reactor, and if possible direct the outlet to exit after them.

This is not only to reduce the solids loading in the refugium, and on the media and in the reactor. But also to make sure any phytoplankton and zooplankton being grown in the refugium (zooplankton more so than phytoplankton, but, with intense light comes algae growth) that are swept out of the refugium make it to the display tank to feed the inhabitants.

If you skim afterwards, the live feeds you are trying to promote will be skimmed out. Pffft to that.

As well as that, the solids will have had a chance to settle out and get caught up in the other reactors and filtration components, so removing as many fines and DOC's as possible prior will help you to minimise this.

Remember this, if you remove as many of the dissolved organics and micro particles BEFORE they get processed by the system, then you minimise overall the amount of solids in the sump, the amount of solids that can return to the system, and the amount of load on other filtration devices.

Addition or absence of ozone

Ozone..... Besides pro-biotics, and calcium hydroxide, is one of my favourite things to use in ALL water treatment systems.

Ozone does so many things that are beneficial to your tank, it's amazing more people don't use it, it is quite affordable these days, and if controlled, can be used very successfully and safely applied to your tank.

When ozone is applied to a system (either into a protein skimmer, or into a reactor that sits near the inlet to the protein skimmer) it achieves a very important function to a skimmer called micro-flocculation.

In a nutshell, it means that particles that are really small, and hard for a protein skimmer to remove, are oxidised and bound together, not only making them easier to remove because they are larger, but also making them hydrophobic (in some circumstances) and therefore more likely to get caught in the bubble plume and be removed.

This is one of the main reasons that light penetration and water clarity is improved when using ozone, it simply allows a higher capture rate of micro particles that cause turbidity in the tank.

If however the skimmer is not big enough to distribute the volume of ozone gas Into the bubble column, or there is simply too much ozone being pumped in too fast, the ozone will reduce skimming efficiency, by breaking the carbon bonds of the long chain molecules and putting them back into suspension of the air bubbles, causing them (the bubbles) to not capture the particles effectively and actually reverse the effectiveness of the skimmer.

So you will be oxidising the waste, you'll just have no way of actually removing it because your skimmer won't be able to.

Below is a link to a table that shows all of these application factors, and depending on what your selections are, and what inputs you put in, will show you what size skimmer you will need, with the specifications required to get the best possible fractionation result.

You Can download this file below from my google drive, and the only cells able to be edited are those which have values you need to edit.

I will point out, that although you may not think it so, Aquarium applications will actually be subject to a higher scrutiny in application and require Higher efficiency fractionators than aquaculture systems. Because it (a protein skimmer) is most often the BACKBONE of both nitrate and phosphate reduction, (which, more often than not, is not considered a priority in Aquaculture systems where fine solids removal and water clarity is the main priority), a higher percentage of biomass REMOVAL (especially in Organic carbon driven systems) is required and therefore adds another aspect to an aquarium application that needs to be addressed.

Finishing up this post, I hope that one day, skimmer manufacturers will actually state dwell times, turnover rates and system passes for their skimmers in relation to water volumes, at the very least I hope that you will find some assistance and worth in this information.

Although this information will give you the knowledge you need to understand skimmer design, wisdom will allow you choose which factors are more important than others in your particular application, therefore, Use this table wisely, you don’t need all of the factors to be spot on, just within acceptable ranges, unless of course you have disposable income, then by all means (if your tank needs it) go for the skimmer that is going to deliver the most effective result by sizing all the factors at optimum.

There is a difference between knowledge and wisdom, for instance, knowledge is knowing tomato is a fruit, wisdom is not putting it in fruit salad.

And that is this posts words of wisdom.

Enjoy your tanks, and I hope that the information and content I am providing is at least helping you and your family produce a tank that you can all enjoy.

And lets face it, if you are all happy, and your not constantly forking out cash to try and fix problems by avoiding them in the first place, then you are much more likely to get a sandwich and a coffee made for you. 

And that my friends = WIN!