Nutrient reduction using Organic Carbon - Nitrate deficiency

A phrase I hear all too often is, organic carbon dosing (whether it be referring to vodka, Vodka vinegar sugar dosing/VSV, Commercial supplements like zeofood/ReefBiofuel/NO3:PO4X or Bio-pellets) reduced my nitrate to Zero but doesn't reduce phosphate, so i have discontinued/taken them offline, OR, so i am running GFO, or some other phosphate absorbing product in conjunction with it.

In any marine system that is already, or will possibly use, a bacterial driven system to reduce nutrient (I.E. organic carbon dosing) it is usually (NOT ALWAYS, but more often than not) organic carbon limited. That means, for bacteria to take up nutrients and waste, they need an organic carbon source in order to reproduce more and take up more nutrient.

A certain amount of organic carbon is liberated when organic wastes are broken down by bacteria (and the enzymes they produce) but more often than not, there is not enough organic carbon liberated in relation to nitrate and Phosphate levels in the aquarium for bacteria to reduce these nutrients as well.

And thus, you need to add more organic carbon.

Now when you add organic carbon, you get an increase in bacterial production and an increase in nutrient uptake by bacteria, let me say right now, that an efficient protein skimmer processing a good portion of the overall system volume and flow is ESSENTIAL to remove this bacteria.

When bacteria proliferates, it takes up more nutrient, and to get the nutrient out, you need to remove the bacteria through protein skimming.

Enter the redfield ratio. Now, let me be the first to say that this doesn't exactly apply to Bacteria, it mostly applies to phytoplankton nutrient uptake, and bacteria may take up levels of organic carbon:nitrate:phosphate differently to phytoplankton, but it has been proved time and again that applying this rule to organic carbon dosing works.

The redfield ratio is:
106:16:1, OR 106ppm Organic Carbon to 16ppm nitrogen to 1ppm phosphorus

In simple terms, in order to accelerate uptake of nutrient by addition of organic carbon, you need 106ppm of organic carbon to reduce 16ppm of nitrate, and you need 106 ppm of Organic carbon and 16ppm nitrate to reduce 1ppm of phosphate.

As i said, the ratio is not exactly this, and there are other elements like iron, that are believed to be involved, but the general idea to keep in mind is that you need organic carbon, nitrate and phosphate in these types of ratios to reduce overall nutrient.

It is believed, and i must say i agree to a certain extent, that bacteria need both nitrate and phosphate (and organic carbon obviously) to reduce them both effectively. Now there are certain types of phosphate (and indeed nitrate) specific bacteria that will mostly only target either nitrate or phosphate, and these are commonly included in good probiotic bacterial mixes (more on this later in another post) and do help, and can be an exception to the redfield ratio and the belief that bacteria need both nitrate and phosphate to reduce both effectively, but in general, and for the most part, the redfield ratio still applies.

Thus, looking at the redfield ratio, you can see that nitrate is very easily reduced, and phosphate isn't, and so when people say, "all my nitrate is gone but my phosphate is still high", it is not that organic carbon dosing is not working, it is that the entire requirements of an organic carbon dosing system are not being met. In other words......... YOUR NITRATE LIMITED BROTHER!!!!!!!!!!

Simple solution, add more nitrate! AND possibly more organic carbon. obviously if your nitrate limited you need to add nitrate to remove your leftover phosphate levels, but, if the level of phosphate is too high, then just like to remove phosphate you have to add more nitrate because you are nitrate limited, you may have to add more organic carbon simultaneously as by increasing the ratio of nitrate to phosphate, you may have also decreased the ratio of organic carbon to nitrate, and therefore may have (to a certain extent) become organic carbon limited again.

I personally have reduced phosphate levels from 1.6ppm to 0.1ppm in 6 hours using nitrate dosing, I DO NOT RECOMMEND THIS, it is simply an example to show how well it works.

Nitrate can be added in the form of ammonia (adding ammonium chloride), urea, or mixing up a solution of something like potassium or calcium nitrate.

I have personally used Seachem's Flourish Nitrogen to achieve VERY effective nitrate dosing/phosphate reduction in the past, but am now using potassium nitrate alone. Off the top of my head Flourish Nitrogen is potassium nitrate and Urea, and seems to work very very well.

I have also heard of people using ammonium chloride successfully (urea in flourish nitrogen would break down into ammonia and therefore perform the same action). Which is the better option i can not comment exactly but i personally believe that adding ammonia based nitrogen may possibly be better as the elemental nitrogen/nitrate being produced is being done so by bacterial/biological action and may have different ions/enzymes/proteins, amino acids bound with it, or produced in certain ratios to it, that make it a more effective and biologically available form of nitrate/nitrogen, but i cannot confirm this for sure.

It may also be that the nitrogen used by the bacteria to remove the phosphate is not consisted of nitrate ions alone, and the bacteria could be using nitrogen directly from the ammonia or urea, although I have no evidence to back it up, the super fast reduction of phosphate in my above example (1.6ppm to 0.1ppm in 6 hours) may be an insight into this, as the reduction of phosphate happened so quickly, and it was Seachem Flourish nitrogen which was used in this example. this however is open to argument as it also contain potassium nitrate, AND the urea would also have to be broken down into ammonia first, but it is an interesting thought either way.

Obviously adding ammonia based nitrogen needs to be done carefully and slowly.

The things you need to do when entering into an organic carbon/bacterial driven system for nutrient reduction in marine aquaria are:

- know the in's and out's of your particular bacterial driven system (VSV, biopellet) BEFORE applying them to your system i.e. research research research
- stay on top of the nutrient demand, this kind of system, especially when nitrate limited, can possibly need DAILY dosing and attention in order to keep the system stable and operating a low and balanced nutrient level
- have not only a good, but an EXCELLENT skimmer, i cannot stress this enough, in fact, with any marine system, go for the best skimmer you can afford, and aspire to get better if the skimmer you have has shortcomings on your system, it is the backbone of any good marine system.
- have a set of very accurate, high quality test kits to monitor nutrient levels
- and finally, dose these element in accordance with YOUR TANK, not anyone else's, and make changes and additions SLOWLY, every tank is different, albeit the basics are the same, but your tank will run differently, even if every other parameter (water flow, size and design of skimmer, tank size, salt mix etc) is the same, I can almost guarantee that it will run differently in some way or another to any other tank.

On the flip side, something as simple as feeding more and/or adding more fish can increase your nitrate levels sufficiently, but a few things to consider are, your tank may not be big enough, you may not want to add anymore fish, AND feeding more will (however slight) add more phosphate to you tank as well. Any of these reasons may be a good argument to add more nitrate chemically, instead of biologically.

Finally might i say, before applying, or indeed, writing off  a filtration/nutrient control method completely, DO YOUR RESEARCH, it can mean the difference between a excellent system, or total disaster, this applies to using a system incorrectly, and also taking it offline without understanding why it isn't working, and/or addressing the main issues causing the problems or concerns in the first place.

Happy Fish keeping

G