Phosphates are derived from phosphorous, which finds its way into our swimming pool water in different ways. Fertilizer, industrial discharges, decaying plant matter, some detergents, swimmer waste ( urine, sweat, and cosmetics ) and even tap water are all possible sources of phosphates.
After phosphates are broken down into orthophosphates they cannot be oxidized any further, which means our sanitizers ( oxidizers ) are not effective and may make it difficult to maintain a free chlorine reading. Phosphates are a vital plant nutrient that at even low concentrations in your swimming pool water can cause algae growth and increase chlorine usage.
Just because your swimming pool water turns green, it does not mean you have phosphates in your water. Any swimming pool can have an algae bloom if the sanitizer level is not properly maintained or the circulation system is not running long enough for your swimming pool.
Most pool stores can test for phosphates and if they are present can supply you with a phosphate remover and guidelines for treatment. Unless you have phosphates in your fill water, usually there is no need to add a phosphate remover on a weekly basis or as part of your swimming pool maintenance routine.