Optimum Range of Water Parameters for Aquarium Nitrifying Bacteria

Last Updated on December 8, 2018

The existence of nitrifying bacteria is very important in the aquarium as they assist in breaking down the waste. There are many water parameters that affect their activity and growth. Eventually, it affects on system and amount of nitrates and ammonia. High levels of Ammonia and nitrites can be dangerous to Fish and may result in their death.

Aquaponics cycle largely depends on bacteria that convert ammonia to nitrites and then to nitrates. Their growth and health are very important to the aquaponics system.

There are two types of Bacteria

  • Nitrosomonas: Oxidizes ammonia into nitrite. Ammonia and Nitrite are harmful to Fish.
  • Nitrobacter or Nitrospira: Oxidizing nitrite into nitrate. Nitrates are harmless to Fish and are absorbed by Plants

Each strain may have specific tolerances to environmental factors and nutrient preferences not shared by other, very closely related, strains. There is need to keep the parameters in a range which satisfy the needs of both bacteria. This will ensure a healthy system.

Aquarium Parameters for Nitrifying Bacteria

1. Temperature


The temperature for optimum growth of nitrifying bacteria is between 77-86° F (25-30° C).

The growth rate will decrease by 50% at 64° F (18° C). It will decrease by 75% at 46-50° F.

No activity will occur at 39° F (4° C)

Nitrifying bacteria will die at the temperature below 32° F (0° C). or above 120° F (49° C).

Nitrobacter is less tolerant of low temperatures than Nitrosomonas. In cold water systems, care must be taken to monitor the accumulation of nitrites.

Read more about the optimum temperature for aquaponics here

2. pH

The optimum pH range for

  • Nitrosomonas is between 7.0-8.0 [these bacteria process ammonia to nitrite]
  • Nitrobacter is between 7.3-7.5 [nitrite to nitrate]

At pH levels below 7.0, Nitrosomonas will grow more slowly and increases in ammonia may become evident. Nitrosomonas growth is inhibited at a pH of 6.5.

Nitrobacter will grow more slowly at the high pH levels. Initial high nitrite concentrations may exist.

Make sure pH does not drop below 7.0 since nitrification is completely inhibited at 6.0. Care must be taken to monitor ammonia if the pH begins to drop close to 6.5. At this pH, almost all of the ammonia present in the water will be in the mildly toxic, ionized NH3+ state.

3. Dissolved Oxygen

Maximum nitrification rates will exist if dissolved oxygen (DO) levels exceed 80% saturation. Nitrification will not occur if DO concentrations drop to 2.0 mg/l (ppm) or less. Nitrobacter is more strongly affected by low DO than Nitrosomonas.

DO largely depends on other parameters as well. Since warmer water holds less oxygen, water with low PH holds less oxygen, water with poor oxidizing ability holds less oxygen.

Read more about the role of Dissolved oxygen (DO) in aquaponics here

4. Salinity

Saltwater nitrifying bacteria will grow in salinities ranging from 6 up to 44 ppt. (specific gravity between 1.0038-1.0329). Freshwater nitrifying bacteria will grow in salinities ranging between 0 to 6 ppt (parts per thousand) (specific gravity between 1.0000-1.0038).

Adaptation to different salinities may involve a lag time of 1-3 days before exponential growth begins.

5. Light

Nitrifying bacteria are photosensitive, especially to blue and ultraviolet light, until they fully establish a colony. Sunlight can cause considerable harm to the biofilter.

After they have colonized a surface this light poses no problem. During the first 3 or 4 days, many of the cells may be suspended in the water column. Specialized bulbs in reef aquaria that emit UV or near UV light should remain off during this time. Regular aquarium lighting has no appreciable negative effect.

Nitrifying bacteria are photosensitive, especially to blue and ultraviolet light. After they have colonized a surface this light poses no problem. The bulb that emits UV or near UV light should remain off during this time. However, there is no appreciable negative effect of Regular aquarium lighting.

6. Micronutrients

All species of nitrifying bacteria require a number of micronutrients. Minimal levels of other essential micronutrients is often not a problem as they are available in our drinking water supplies. The increasing popularity of high-tech water filters for deionizing, distilling, and reverse osmosis (hyperfiltration) produce water that is stripped of these nutrients. While these filters are generally excellent for producing high purity water, this water will also be inhibitory to nitrifying bacteria. The serious aquarist must replenish the basic salts necessary to the survival of the aquarium’s inhabitants. These salts, however, usually lack these critical micronutrients.

Most important among these is the need for phosphorus for ATP (Adenosine Tri-Phosphate) production. The conversion of ATP provides energy for cellular functions. Phosphorus is normally available to cells in the form of phosphates (PO4). Nitrobacter, especially, is unable to oxidize nitrite to nitrate in the absence of phosphates.

Sufficient phosphates are normally present in regular drinking water. If all the above-described parameters are within the optimum ranges for the bacteria and nitrite levels continue to escalate without production of nitrate, then phosphate block may be occurring. In recent years, with the advent of phosphate-free synthetic sea salt mixes, this problem has become prevalent among marine aquarists when establishing a new tank.

Fortunately, phosphate block is easy to remedy. A source of phosphate needs to be added to the aquarium. Phosphoric Acid is recommended as being simplest to use and dose, however, either mono-sodium phosphate or disodium phosphate may be substituted. When using a 31% phosphoric acid mixture, apply a one-time application of 1 drop per 4 gallons of water to activate the Nitrobacter. This small dosage of phosphoric acid will not affect the pH or alkalinity of marine aquaria.

7. Nutriment

All species of Nitrosomonas use ammonia (NH3) as an energy source during its conversion to nitrite (NO2). Ammonia is first converted (hydrolyzed) to an amine (NH2) compound then oxidized to nitrite. This conversion process allows Nitrosomonas to utilize a few simple amine compounds such as those formed by the conversion of ammonia by chemical ammonia removers.

Nitrosomonas is capable of utilizing urea as an energy source.

All species of Nitrobacter use nitrites for their energy source in oxidizing them to nitrate (NO3).

8. Chlorine and Chloramines

Before adding bacteria or fish to any aquarium or system, all chlorine must be completely neutralized. Residual chlorine or chloramines will kill all nitrifying bacteria and fish.

Most US cities now treat their drinking water with chloramines. Chloramines are more stable than chlorine. It is advisable to test for chlorine with an inexpensive test kit. If you are unsure whether your water has been treated with chloramine, test for ammonia after neutralizing the chlorine. You can also call your local water treatment facility.

The type of chloramines formed is dependent on pH. Most of it exists as either mono chloramine (NH2Cl) or dichloramine (NHCl2). They are made by adding ammonia to the chlorinated water. Commercial chlorine reducing chemicals, such as sodium thiosulfate (Na2S2O2) break the chlorine: ammonia bond. Chlorine (Cl) is reduced to harmless chloride (Cl ) ion. Since dichloramine has two chlorine molecules, a double dose of a chlorine remover, such as sodium thiosulfate, is recommended.

Each molecule of chloramine that is reduced will produce one molecule of ammonia. If the chloramine concentration is 2 ppm then your aquarium or system will start out with 2 ppm of ammonia. Chlorine Remover will reduce up to 2 ppm of chlorine at recommended dosages. During the warmer months, chlorine levels may exceed 2 ppm. A double dose would be required to effectively eliminate the excess chlorine.

Summary of all main Parameters

Organism typeTemp
Warm water fish22–326–8.54–6< 3
Cold water fish10–186–8.5 6–8< 1
Plants16–305.5–7.5> 3< 30
Bacteria 14–34 6–8.54–8< 3

General water quality tolerances for fish, hydroponic plants and nitrifying bacteria

and overall, optimum parameters that satisfy all players of Aquaponics

18–306–7< 15–150> 5


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