Keep your fish healthy and thriving by testing your aquarium water's NO2 levels regularly with this easy-to-use API NITRITE TEST KIT for freshwater and saltwater aquariums. Testing water parameters weekly helps prevent invisible water problems that can be harmful to fish. Nitrite is produced in the aquarium by fish waste and uneaten fish food. Low levels of nitrite inhibit respiration and suppress the immune system; high levels cause suffocation.  The API NITRITE TEST KIT tests for harmful nitrite levels from 0 to 5 ppm. This product comes with one nitrite bottle, one capped test tube, one instruction manual and one color card. API NITRITE TEST KIT can be used in freshwater and saltwater aquariums.