What level of nitrites is toxic to fish?

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What level of nitrites is toxic to fish?

Thu Aug 15, 2019 7:43 pm

Nitrate and nitrite are naturally occurring ions that are part of the nitrogen cycle.

Nitrification is the oxidation of an ammonia compound into nitrite, especially by the action of the nitrifying bacteria called Nitrosomas. The nitrites will then be oxidized to nitrates by the bacteria Nitrobacter.

- Nitrate is less toxic than nitrite and is used as a food source by live plants.
- The process of converting ammonia to nitrate is diagrammed in the nitrogen cycle.
- Nitrification is most rapid at pH of 7-8 and at temperatures of 25-30°C.
- Nitrification causes waters to decrease in pH.

Nitrite levels above 0.75 ppm in water can cause stress in fish and greater than 5 ppm can be toxic.
Nitrate levels from 0 – 40 ppm are generally safe for fish. Anything greater than 80 can be toxic.

Note: A full cycled aquarium should have 0 nitrites reading.