Key Parameters - Nitrite

In the presence of oxygen a naturally occurring species of bacteria Nitrosomonas spp. converts ammonia into nitrite (NO2-). This process is the first step in the conversion of ammonia to nitrate (NO3-), it is known as nitrification. Nitrite is much less toxic than ammonia. Levels above and in the range of 10 –20 mg/l are lethal to many species. Nitrite toxicity decreases as the availability of mineral salts increases.

The process of denitrification continues as Nitrobacter spp. of bacteria oxidise nitrite into the less toxic nitrate ion (NO3-). Nitrate is toxic to fish at levels above and in the range of 50-300 mg/l depending on the specific fish species.