Phosphates are food for algae. Excessive phosphate in the water can cause cloudy water, algae growth, and sanitiser demand. Phosphates can enter the pool from fertilisers, human and animal wastes, and debris. Acceptable levels are 0 – 0.3 ppm.

Levels of phosphates high enough to cause problems are unusual. Often, if a pool has one of the above problems, it is due to inconsistent maintenance or inadequate filtration. However, if it is determined that phosphates are a problem, it will be necessary to perform a partial drain. Phosphates do not break down naturally.  The other option is to use a proprietary phosphate remover, which uses lanthanum to precipitate the phosphate as a white, insoluble compound.