Phosphates in Swimming Pools

Stuborn Algae problems could be due to high levels of phosphates in your pool or spa, here's some good info from Ask Alan.

Phosphates can increase the likelihood growth of algae in swimming pool water and can enter the water from such sources as: decaying plant matter, fertilizers, mineral treatment chemicals, contaminated well water, acid rain, contamination with soil, ground water runoff, bird droppings, bather wastes, urine and sweat. Phosphate is a vital plant nutrient and the presence in swimming pool water, even at low concentrations, can cause accelerated algae growth in poorly maintained pools. Pools, that are properly maintained, usually do not have unexpected difficulty controlling algae, even in the presence of phosphates. Higher levels of phosphates can make algae control more difficult and increase the amount of sanitizer required to maintain satisfactory control of algae. It is possible to remove modest levels of phosphates, by treating the pool water with a phosphate precipitating lanthanum product. Very high levels may require so much of the lanthanum compound, as to render this approach impractical, unless there is no option of water replacement. In order for phosphate reducing products to work the concentration of phosphates must be reduced to extremely low levels: parts per billion. The benefits of such product use is adding another layer of protection against algae growth. Proper pool water maintenance is always the first line of defense. Testing for phosphates is not universal, but in those cases where algae control is proving difficult, despite apparently ideal pool water conditions, testing for phosphates and nitrates might be advantageous.