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Ammonia, pH and Nitrite

Ammonia and pH 

Did you know that the toxicity of ammonia increases with the increase of pH? It's true. The more alkaline the water, the more toxic the ammonia. This is why ammonia poisoning occurs with such frequency in brackish, African Cichlid, and especially salt water tanks, and why testing for ammonia is so critical.


Another significant water quality parameter

    How many times have you tested an aquarium in which you have been experiencing fish losses and found the water quality within the parameters described by industry standards? Though you find the specified pH, no ammonia, and the proper salt level, you still may be dealing with a devastating water chemistry problem. 

   What could this problem be? Most likely, an excessive level of Nitrite (NO2) is the culprit. What is it? How did it get there? 

   As we know, the "Nitrogen Cycle" takes place everywhere- in fresh water, salt water, and even in our back yards. What is it? Here is a brief description. Ammonia, from decomposition of organic materials, is converted by bacteria called "nitrosomonas", "nitrobacter" and others to the relatively less harmful nitrate. 

   In the aquarium, ammonia is converted to nitrite by nitrosomonas and other bacteria, nitrite is converted to nitrate by nitrobacter and other bacteria. Problems occur in new aquaria where there are too few of these helpful bacteria, and the tank is populated too quickly, and in older aquaria when there is a sudden population increase. Development of nitrifying bacteria is in direct proportion to the bio-load (or number of fish in a tank). 

   The ensuing overabundance of ammonia, created by fish waste, uneaten food, dead fish or decaying plants may be converted to nitrite by nitrosomonas, but when there are not enough nitrobacter to successfully convert nitrite to nitrate, a problem develops. It is important to note that the conversion requires a high amount of oxygen in the water to make the process work.


Our recommended pH of 6.8 - 7.0 for fresh water incorporates this important concept. In areas of the Northeast where tap water is hard and alkaline, you should understand this aspect of water quality, and how to cope with it.




The clinical signs of nitrite poisoning are gasping, hanging, and/or improper swimming behavior, changes in coloration, an increase of mucous production on the skin, and protruding and/or cloudy eyes. In extreme cases, death may occur when excessive bacterial bloom prohibits oxygen from dissolving in the water. 

   Ammonia or nitrite poisoning can also impair the immune system by interfering with normal metabolic activities. This causes increased susceptibility to almost all pathogens, the most common being columnaris and Ich. Freshwater fish deaths can occur just as easily from nitrite peaks as ammonia peaks. Some fish are more nitrite-tolerant than others, like serpae tetras. Guppies and other live bearers are more nitrite sensitive because they take in nitrites which poison them. In other fish, the addition of one teaspoon of salt per gallon in a freshwater tank will help prevent the intake of nitrites. 

   When setting up a new aquarium, it is best to start with only a very few fish, and add fish slowly.  Allow 4 to 8 weeks for the nitrifying bacteria to reproduce and reach a population level that is able to successfully convert all ammonia and nitrite to nitrate. The addition of live aquatic plants helps remove nitrates, as it is plant food. 

   To keep a biological balance in the established aquaria, we recommend 25% water changes every 10 to 14 days, and changing the filtering materials. The latter should never coincide with the water changes, as the friendly bacteria which live on these materials would be eliminated, and could cause an imbalance that would allow ammonia and/or nitrite to reach a toxic level. If the filter medium has a large surface area, more nitrifying bacteria develop, and the aquarium can handle a heavier bio load (more fish).

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