Nitrate / Nitrogen



Besides phosphate, nitrate (NO3-) is the most important nutrient in reef aquaria. Ammonium, which is produced from decomposing proteins, is oxidized by bacteria via nitrite to nitrate and reduced again under anaerobic conditions by denitrifying bacteria. Corals can use some intermediate stages of nitrogen. If nitrate is not detectable in an aquarium system, this cannot necessarily be considered a proof for a nitrogen limitation in the respective aquarium.

What is this?

Corals can utilize nitrogen in several forms (ammonium, urea or nitrate). The nitrogen cycle, in which nitrogen is biochemically converted, is one of the most important biological functional cycles in nature. Nitrate is the highest form of oxidation of nitrogen. A breakdown of the biological control circles in an aquarium is almost always accompanied by a disturbance of the nitrogen cycle. Therefore the supply and care of the bacteria (“biofime”) of the aquarium is very important.


Above all, the relation of the nutrients to each other is relevant. The individual value itself is not most important. Depending on the biotope, the nutrients should be adjusted appropriately and pay attention to a ratio of NO3– to PO₄³⁻ in the factor 100 : 1.


Regular control of the nitrate value, if necessary adjustment by adding or reducing by the mentioned measures.

Indicator species:

Many leather corals do not fully open their polyps at higher nitrate levels. Above 20 mg/l (0,26 Clavularia viridis loses its green fluorescence. In the case of nitrate deficiency, red Montipora species develop colour loss, and some Acropora species lose polyp tissue from the base. Nitrogen deficiency makes the entire reef tank look colourless, dull and greyish. Corals prefer to take up nitrogen as ammonium, while nitrate must first be reduced before uptake.

Value too high:

Reduction of feed input, control of skimming and filtering, mud siphoning/replacement of substrate, installation of zeolite filtration, installation of pellet filters. Dosing Bacto Blend and Bacto Energy.

Value too low:

Dosing Elementals N, Sprint, Feeding fish with Protein Power Food.

Variety Nutrient
Benefit Yes, essential
Default value 0,5–2 mg/l (0,26
Skill Level green
Source Feed, phytoplankton, additives
Available Elementals N, Coral Sprint, Amin
Importance 1–6 5
Detection quality high
Relation values phosphate

Balling Light:

In the Balling-Light system, no nutrient input is made in the basic supply. Lime supply and nutrient input are strictly separated. The basic dosage via organic/amine and normal feed dosage via coral and fish feed is usually sufficient. Acute nutrient limitations can be compensated for with Elementals P and N.

Nitrogen is present in the aquarium in numerous different forms: ammonium, ammonia, nitrite, nitrate and a large number of nitrogenous organic compounds. Nitrate does not necessarily have to be the dominant form of nitrogen, but it is our measured variable, which is recorded by drop or laboratory tests. This is also sufficient for assessing the nutrient balance, even if not all forms of nitrogen are recorded this way. Please note, however, that the ratio between phosphate and nitrate should be around 1:100.

Measuring technology

Nitrate can only be measured indirectly in seawater with normal drop tests. In the test procedures, the nitrate is reduced to nitrite with an acid and measured and then, depending on the test, extrapolated back to nitrate. In most test procedures this leads to a disturbance of the measurement results if there is an increased amount of nitrite in the tank. Special seawater tests such as the AquaHometest from Fauna Marin have a compensation table and take into account the influence of nitrite in order to achieve accurate measurement results. In the laboratory, nitrate is measured directly from seawater using ion chromatography. Although this measuring method is very complex, it leads to highly accurate measurement results.

Nitrogen in nature

Only small amounts of nitrogen (less than 0.3 mg/L) are found in the reefs. The deeper one dives down, the higher the nitrate reading becomes, which of course has an effect on the animals living there. While it is hardly detectable at the water surface, it rises to values of up to 3 mg/l with increasing water depth. However, the distribution of nitrogen in the water does not only depend on the depth, but also on the particular habitat of the region or biotope you are looking at. In coastal areas the nutrient levels are generally higher than in atolls in the open ocean. Even in the inner and outer reefs there are often considerable differences.
The majority of the nitrates present in the reef originate from organic compounds such as the decomposition of dying plankton or the decomposition of long-chain molecules. In the aquarium, it is leftovers of fish food or the ammonium that fish continuously release into the water through their gills, where it is then oxidized by bacteria in the course of their metabolism via nitrite to nitrate.

Nitrogen in the aquarium

Corals and a variety of other organisms can metabolize and absorb nitrate directly. Besides bacteria, these are mainly organisms that carry out photosynthesis. However, this does not mean that a high nitrate level will result in more growth.

More important than the value itself is the correct ratio to PO₄³⁻ and other phosphorus compounds.
Nitrate in seawater is not toxic to fish. However, aquarium experience shows that fish feel comfortable if the value is not too high. In any case, make sure that the nitrate value is not set below the PO₄³⁻ value (ratio phosphate/nitrate about 1:100), because this creates a relative lack of nitrogen, which quickly leads to problems. Nitrate is mainly caused by the decomposition of substances that enter the aquarium via the food and additives. Tap water or a defective osmosis system can also cause the nitrate level in the aquarium to rise. Other sources can be dead fish, snails, or algae or cyanobacteria coatings that dissolve.

Reduce nitrate concentration

There are various approaches to reduce the nitrate content in the aquarium. In each of these measures, however, attention must also be paid to the phosphate level, as this also corresponds to the nitrate level.


An adapted fish load is a basic requirement for a healthy aquarium. Fish and other animals increase the nutrient concentrations through their metabolism. Reduce the stocking level so that less food gets into the water and make sure that the nutrients are exported sufficiently, e.g. by vigorous skimming and regular partial water changes. When feeding plants such as lettuce, dandelions and others, remember that they bring nitrate into the aquarium.

Too little light, incorrect water values or a lack of trace elements can have an influence on the growth of the animals, and this also increases nutrient concentrations. Low coral growth is often the result of reduced performance of lights, skimmers, flow pumps and filters.


Bacteria and carbon dosage can be a proven means of controlling nitrate concentration. In this case we recommend the dosage of Bacto Reef Blend and Bacto Energy to feed the bacteria. Also make sure that there is sufficient skimming, if necessary in combination with the Zeolight system. This system is especially suitable for the particularly nutrient-poor biotope systems such as the offshore biotope or pure SPS aquaria.

Filter media

Filter media such as activated carbon and zeolites can be very helpful in keeping nutrient concentrations low, especially in combination with bacteria and bacteria feed. Please refer to our biotope recommendation Offshore.

Activated carbons remove larger amounts of organic structures that may contain nitrogen. Zeolites bind trace elements as well as ammonium and thus reduce the precursors to nitrate. Zeolites are also helpful because they have a particularly suitable surface for bacteria. These bacteria bind various trace elements and nutrients. Through the regular movement and circulation of the zeolite material, not only sediments are removed, but also biofilms, which are then skimmed off, which represents an additional export of nutrients.


Solid carbon sources like NPO Redu Pellets are also an effective way to reduce high nitrate levels. These are special solid carbons that are used to break down nutrients in a specially developed filter in the technical tank.

Raise nitrate level

Should there ever be a nitrogen deficiency, it may be necessary to effectively increase it. This is possible with the preparation Elementals N (functional nitrogen solution). By feeding Protein PowerFood you increase the nutrient content of the aquarium by feeding the fish. The special composition of the feed ensures that the correct ratio of nitrogen and phosphorus is added to the water in increased quantities. Alternatively, the fish and snail population can be increased. Reducing skimming and/or zeolite filtration also has this effect.


Often, weak skimmers and too high fish density are the reason for a high nutrient concentration in the reef tank. Always focus your nitrate and phosphate at the same time and pay attention to the correct composition of the community of tank inhabitants. With the usual systems, the nutrients can then be controlled well. With skimmers there are big differences in performance. For example, orientate yourself on the models that professional breeding farms use because you will not do anything wrong installing those to your tank. If you save on water flow and skimming at the beginning, you will need to dig much deeper into your pockets later to get problems under control.

In some analyses the sum parameter TNb is given. The total nitrogen bound (TNb) indicates a total nitrogen load of the system. This nitrogen can occur in the form of ammonia, ammonium salts, nitrites, nitrates and organic nitrogen compounds. During the measurement, components of corals and fish food as well as water care products or decomposition products are also measured.

Tip 2:

The excretions of the fish are the best coral food. Fish exhale nitrogen as ammonium, and corals like to use this source because they can use this form of nitrogen directly. The other excrements of the fish are also used. Good feeding of the fish is therefore very important, if one wants to achieve optimum coral growth and thus has a nutrient regulation. Important here are feeds of the new generation (genuine soft granules with a very high content of proteins and fats, provided that these are mainly derived from unsaturated fatty acids). It is also very important that you use feed that is made from whole fish and/or shrimp. Soy or other substitutes are less suitable as they quickly enrich the water with nutrients and inhibit coral growth.

In summary, good nutrient conversion by the corals supports the stability of the nitrogen cycle and thus also the carbon cycle, which keeps the pH stable during nitrogen conversion.