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?
LOGIC.
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:
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.
DIAMETER:
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?
NO,..
just.....no.
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)
AND
2. Will the skimmer impact the result of that filtration in
a positive or negative way if skimmed afterwards.
1.
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.
2.
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)
NEGATIVE IMPACTS:
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.
https://drive.google.com/file/d/0BxSbloysP69YTlRWR3dIUlFIODg/edit?usp=sharing
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!
