API Ammonia Test Kit measures ammonia to help prevent any fish loss, as ammonia is the number one stress factor and killer of aquarium-kept fish. Ammonia is released into an aquarium in the forms of uneaten food, decaying organic matter, and when fish release it through their gills, urine, and solid waste. The API Ammonia Test Kit is a mercury-free, salicylate test for fresh and saltwater fish, and measures ammonia levels from 0 to 8 ppm.