5.3. Safe Nitrite Levels

Nitrites are products of the decomposition of food proteins. Nitrite is not a poisonous as many would have us believe. The acute toxicity is where the fish die in hours or days. This is the “Toxic” level in the chart below. The chronic toxicity is where the fish will have diseases and a general “failure to thrive”. This is the “Alarm” level below.

pH of the waterAPI nitrite test in ppm
pHAlarmToxic
6.60.52
6.80.52
7.014
7.21.56
7.428
7.628
7.82.510
8.0312
8.23.514
8.43.514
8.6416

One should strive to keep nitrite levels undetectable not because nitrite is so poisonous, but because what amounts of nitrite in the water indicate about the aquarium filtration. Like ammonia, undetectable nitrites means you have a healthy aquarium with low bacterial counts. And the bacterial count in the water to be the most important water variable that there is in an aquarium.

Nitrite is the second product in the nitrogen cycle, with ammonia being the first. The presence of nitrite in an aquarium generally indicates a aquarium which is cycling. Note that sometimes cycling skips the nitrite step and goes straight to lots of nitrate and no ammonia and no nitrite.

One solution for nitrite spikes is to add a small amount of salt. The chloride ion competes with the nitrite ion for absorption into the gills so the fish are protected against the nitrite. For the dosage measure the nitrite level in parts per million (ppm). Divide the ppm by four. This is the number of level tablespoons to put into each ten gallons of aquarium water to detoxify the nitrite.

tropical fish photo Dicrossus filamentosus, checkerboard cichlid
Mesoheros festae, Red Terror Hybrid

There are some aquarium hobbyists who are interested in delving deep into the science and the calculations behind all aspects of the hobby. For those who are so inclined the following is pertinent:

5.3.1. Nitrite in More Depth (links to aquariumscience.org)

Note that conditioners such as Prime do absolutely nothing for nitrite toxicity. That is simply “snake oil” marketing hype by Seachem. Here is a link to an analysis of Prime and Safe:

5.5.3.2. Prime and Safe (links to aquariumscience.org)


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Translated in dutch by : Joost Abrahams
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