Phosphate, which is PO4 (that is one atom of phosphorous and four atoms of oxygen), is an essential trace compound in reef aquariums that is used in protein synthesis. In an aquarium, phosphate levels can get high and that opens the door for potential problems. The three biggest problems one can face from high phosphate are: 1. Algae blooms. Lack of phosphate in the water is one of the bottlenecks of algae growth. Remember it’s less than 0.05 ppm. When phosphate levels rise algae can grow out of control. 2. Coral Appearance. High phosphate can cause browning of corals as it promotes the proliferation of zooxanthellae which typically is more brown in color. 3. Phosphate can directly inhibit calcification. This is a big problem if you are like me and trying to grow lots of stony corals. If the phosphate is high, what can we do about it? There are actually a lot of different potential solutions to this problem.