Nutrafin Nitrite 0.0 to 3.3 Mg/L for Fresh and Saltwater, 75 -Tests Suitable for freshwater or marine aquariums to determine nitrate level (0.0-3.3 Mg/L) Best used with Biological Aquarium Supplement, Nutrafin Cycle to determine nitrate level (0.0-3.3 Mg/L) Essential in monitoring your tanks water quality Nitrite should be tested on a weekly basis as it is a toxic and potentially lethal nitrogen compound for fish Easy to follow directions; Contains 75 Tests