Nitrate is the end product of aerobic remineralization. Phosphate and ammonia are waste products of remineralization and produced by dissimilation, the production of the energy needed to break down the organics to become useful and to be used to grow and multiply. Most carbon is released as CO2, closing the carbon cycle. If all this takes place in a biofilm, one has a nitrifying biofilm, which may export +- 15% of the nitrogen processed by the biofilm as N2, this way closing the nitrogen cycle. To have control and be able to manage the nitrogen content we use a biofilter.
Bacteria and algae, most micro life, prefer ammonium-nitrogen as a nitrogen source as when using nitrate a lot more energy is needed and growth is limited. The use of nitrate-nitrogen slows down growth rates.
An aquarium with a lot of fish has a high remineralization rate producing DOC ( dissolved organic compounds) for maintaining heterotrophic growth needed for remineralization. +- 85% of digested food will be released, most nitrogen directly as ammonia and some urea. DOC is then used ( bacteria only can use DOC as a carbon source) and be broken down into its basic building materials which can be reused for growth.
To create a balance the protein content and C/N ratio of the food added is important as it will be determent for the heterotrophic/ autotrophic ammonium reduction ratio, determent for the carrying capacity of the system. It is also important the food is from marine origin otherwise a lot of detritus may be left over after remineralization. Algae may contain a lot of carbon, influencing the C/N ratio when consumed.
A very good skimmer does remove very little protein, it removes mainly DOC but very selective which results in a max removal ratio of +-30%. A skimmer leafs all free inorganic nitrogen and phosphate behind (
ref:CMFDeHaes2018)
Already a lot of energy has been produced to reduce TOC into DOC, all DOC removed by a skimmer is a waste of not only energy but also of the produced inorganic nutrients which stay behind.
How come little nitrate is measured and a lot of phosphates are present? Is nitrate not present because the nitrifiers are outcompeted for ammonium due to a too high C/N ratio? A lot of products for battling nutrients, algae, and cyano may contain a lot of organic carbon, even carbohydrates. Sometimes one is increasing the C/N ratio too high without knowing.
In a reef aquarium with a lot of calcium carbonate rock ( Aragonite) a lot of phosphates may be produced due to disolving rock or sand, nitrification taking place on the aragonite substrate produces acids, or in a CO2 calcium reactor. Calcium and phosphate may produce calciumphosphate as may be seen when using kalkwasser. Phosphate is used for calcification, for making rock. Is the production and removal rate out of balance?
Using high protein food will lower the C/N ratio, increasing nitrification.
Feeding algae may increase the C/N ratio. If a lot of algae eaters are present, less nitrate may be produced.
Please do not add nitrate. Why one should add nitrate?
Nutrient levels are in most cases the messengers, not the cause of problems, exempt when not available. Increasing levels are the indication of underlying problems. Battling them without correcting the underlying cause will not solve a thing. What is measured is what is left over, which is not used at the moment of measuring. In the microworld, the demand can be doubled in a moment as growth is logarithmic.
The presence of phosphate increases calcification rates if enough CO3 is present.(
ref:CMF De Haes En Co 2007- 2020)
A low nitrogen level limits the risk for phosphorus starvation during periods of increased growth. It has been shown phosphorus starvation is the main cause of coral bleaching during periods of increased growth ( increased temp) supported by nitrogen availability, also in aquaria. Therefore, to prevent the nutrient reserve may become responsible for phosphorus starvation, phosphate is best not the growth limiting factor and we keep the nitrate level at max 9X the phosphate level present. It has also been shown insufficient phosphorus supply may harm, even kill corals after a short period of time, insufficient nitrogen availability will harm corals after a much longer period of starvation. that is why we prefer the nitrogen reserve to be the growth-limiting factor.
The coral holobiont.(ref:Anthias2019)
Battling or killing the messengers will not win wars and not solve a thing. In a lot of cases, the method used for battling nutrient levels may cause a lot more problems as an increased nutrient level ever will.
The best way for managing the nutrient content is by using a biofilter, a refuge for culturing your own food, algae or plankton, even shrimp. This way nutrients can be removed as desired by feeding for the target nutrient(s) modified F2 media. For example for removing phosphate, for phosphorus corrected F2 media is used to feed the culture. The culture will be harvested and be used as a food source. (
ref:CMF De Haes En Co 2017-2020) The use of bioflocs?
