Excess nutrients can lead to poor water quality very quickly. If not controlled, phosphate (PO4) can rapidly build up in aquariums from fish waste and uneaten food, decomposing algae and other organic matter, and aquarium supplements and tap water that contain phosphate. Phosphate is important to the aquarium in many ways, but when it accumulates too rapidly it can contribute to undesirable algae blooms. In saltwater systems, high phosphate can also affect the calcium and magnesium levels, inhibiting proper coral growth. Conversely, too low phosphate can limit nitrifying bacteria’s ability to convert nitrite to nitrate. Phosphate is also necessary for aquatic plants to photosynthesize.