Phosphates are salts of phosphoric acid, which is considered a pollutant. Phosphates in water contribute to algae blooms in the same way nitrates do. The greater amount of phosphate, the greater the potential for algae growth and severity of the bloom.
Phosphates enter pools on rain, dust, dirt, leaves, debris, animal fur and soap residue on bathing suits. Phosphates interfere with pool chemistry, and ‘eat up’ the available chlorine, paving the way for algae. The longer organics sit in the pool, the more phosphates are released into the water. Phosphates are in turn algae food, which continues the ‘high phosphate/algae cycle’.
Unless the high phosphate condition is treated, the pool will need to be shocked if the chlorine level is at zero when the pool is serviced. Usually, 1# of shock works, unless there is algae present; in this case, 2 – 5# of shock would be required. As pool owners, we don’t have much control over the dust and rain that get into the water, but removing leaves and debris regularly is one way to help prevent the buildup of phosphates in the water, since the longer the debris sits in the water, the more phosphates can be released.
When a pool is treated for high phosphates, any active algae must be killed first before the phosphate treatment is added. (Algae gives off phosphoric acid as it dies, increasing the phosphate levels again). We prefer BioDex Plus, a commercial grade phosphate remover which is very concentrated.
A 32oz bottle of Biodex Plus will remove 3,000 ppb of phosphates in a 10,000 gallon pool. Whereas, a 32oz bottle of Phosfree (sold at local stores) will only remove 600 ppb of phosphates. The phosphate remover will most likely cloud up the water at first. It will clear out as the phosphates filter out as the water circulates during the regular filtration cycle.
You may purchase Phosfree at your nearby pool store, which is less expensive but not as concentrated.
Cartridge filters do need to be cleaned after adding the phosphate remover.
Sand and DE filters can be backwashed.