Keep your fish healthy and thriving by testing your aquarium water's PO4 3- levels regularly with this easy-to-use API PHOSPHATE TEST KIT for freshwater and saltwater aquariums. Testing water parameters weekly helps prevent invisible water problems that can be harmful to fish. Phosphate enters the aquarium from fish and invertebrate waste and decaying organic matter, such as dead algae and uneaten fish food. Excess phosphate contributes to unsightly algae and green water blooms. In saltwater, excess phosphate can inhibit the growth of hard corals. API PHOSPHATE TEST KIT for freshwater and saltwater aquariums contains two phosphate test bottles, test kit instructions, one capped glass test tube, and two color cards to accurately measure phosphate levels in fresh and saltwater aquariums.