Where are the phosphates coming from?
Phosphates can be introduced into swimming pool water via a multitude of sources, including fertilizers, organic debris, soil, detergents/cleaners, tile cleaners and metal-sequestering chemicals. It can also be deposited through human perspiration and urea (NH2) 2CO.
There are several different forms of phosphate, depending on the source; however, eventually it becomes a form of orthophosphate. Metal products are one of the main culprits that cause failure in salt chlorine generators. This is because staining from metals is more prevalent in salt chlorine pools, due to potential galvanic corrosion from the high total dissolved solids (TDS) of the salt and dissimilar metals present in the water.
As a result, most salt chlorine generator manufacturers recommend using a metal-sequestering agent. However, many of these products use phosphonic (C-PO[OR]2) or phosphoric-acid (H3PO4)-based formulas. When added to a salt pool, they will break down the phosphate to free orthophosphate, which causes problems with the chlorine generator electrodes. As such, it is best to use a phosphate-free metal sequestering product.
Removing the phosphates
Phosphates can be easily removed from pool water by using a phosphate remover. Orthophosphates in pool water exist in a soluble form; the most effective phosphate removers work by turning soluble orthophosphate precipitate into a solid. This will cause some water cloudiness, which can be readily filtered out with a clarifier. However, keep in mind that the more phosphate used, the cloudier the water will become. In extreme cases, it can take up to two to three days for the cloudiness to clear completely. During this cloudy period, it is important to turn off the salt chlorine generator; liquid chlorine can be used in the interim to keep the residual up.
The other option for extreme phosphate levels (e.g. near or more than 5,000 ppb) is to drain and dilute some or all of the water. This method may be better used for commercial pools, where shut down time is limited and cloudiness of the water is regulated. In these cases, it is advisable to dilute out as much phosphate as possible and use maintenance doses of phosphate remover to manage levels.
