API Phosphate PO4 Freshwater & Saltwater Aquarium Test Kit, 150 countPhosphate can enter your aquarium through tap water, fish waste, and decaying organics such as uneaten food and dead algae. Excess phosphate contributes to unsightly algae and green water blooms, and in saltwater, excess phosphate can inhibit the growth of hard corals. The API PHOSPHATE TEST KIT tests phosphate levels from 0 to 10 ppm so that you can easily monitor the condition of your aquarium water and may be used in both fresh and saltwater