Fish can be sensitive to elevated nitrite levels, which makes it important for aquarists and fish keepers to monitor nitrite levels in their aquariums. High levels of nitrites can cause a variety of health issues for fish, including reduced appetite, difficulty breathing, lethargy, and even death. Generally speaking, the longer a fish is exposed to high nitrites the more likely they are to suffer long-term health issues or die prematurely. The amount of time that a fish can survive with elevated nitrite levels depends on several factors such as species of fish, size/age of the individual fish, water temperature and pH level in the tank. In general, most healthy adult tropical freshwater species will live anywhere from 6 weeks up to 3 months when exposed to moderate amounts of nitrites (0.5ppm - 2ppm). However if exposure continues beyond this period then mortality rates increase significantly due largely increased stress placed on the immune system and internal organs resulting from constant exposure over an extended period