sera test NO2 nitrite for the xact determination of the nitrite content in fresh and marine water. The test ist sufficient for approx. 75 test. Useful bacteria convert ammonium to nitrate via nitrite. Nitrite, the intermediate of the pollutant breakdown, is a strong blood poison which often enrichs in newly set-up aquariums. By using of the sera nitrite-test it is easy to determine the level of toxic nitrite. In a aquarium with a good working biological filter, the nitrite level should be 0.