What Is Nitrite?

Nitrite is the second stage of the nitrogen cycle in your aquarium. It usually occurs after ammonia is converted by bacteria to nitrite. More specifically, when ammonia-oxidizing bacteria (AOB) oxidizes ammonia. Oxidized ammonia is, as you probably guess, nitrite. This is sometimes explained, more simply, as bacteria “eating” ammonia and producing nitrite as waste – which is an oversimplification, but true enough, I suppose. 

Some AOB include:

• Nitrosomonas europaea
• Nitrosospira multiformis
• Nitrosomonas ureae
• Archaea species

Although nitrite commonly comes from oxidized ammonia, it can also come from fish food, fertilizers, or your tap water. It’s almost as toxic to fish as ammonia, but not quite. Nitrite is commonly confused with nitrate – which is oxidized nitrite.

A healthy aquarium will have nitrite levels below 5 ppm, ideally. At 10 ppm you may start to see algae issues and around 50 ppm you’ll likely start to see fatalities.