Tetra test nitrite kit is suitable for freshwater and marine aquariums and includes up to 45 testsr nitrite is produced from the breakdown of ammonia in the filter nitrite is highly toxic to fish but is usually removed from the water by the bacteria which live inside the filterr however in new tanks or if the filter bacteria are damaged the nitrite level may become toxicr regular testing especially in new aquariums will prevent damage caused by nitrite poisoningr how it worksr the tetr