Phosphates, Food for Algae, Food for Thought

Phosphate became a household word in the 1970’s when people started to use low-phosphate and phosphate-free laundry detergents. This was to protect lakes, streams, wetlands and other runoff areas from the detrimental effects of excess phosphate. One of these effects is unwanted algae blooms.  What’s true for lakes is also true for swimming pools.


Phosphates are derived from phosphorous, the 11th most abundant mineral in the earth’s crust. It makes its way into pool and spa water from a variety of sources, including fertilizers, swimmer waste (sweat and urine), decaying vegetation, cosmetic items, detergents, and even tap water of many cities (which contains compounds used to treat corrosion).  Phosphates can also be found in many pool products such as stain removal products. Phosphate is persistent and does not break down naturally.


Phosphates are a food source for all strains of algae and can make controlling their growth difficult. Not removing the phosphates will cost you more time and money on maintenance.  Remove the food, and you have a strong weapon against algae.


When excess phosphate is present in a swimming pool, the symptoms often include the following:

  • Cloudy, Green Water
  • Slippery and Slimy Surfaces
  • Mustard and Green Colored Debris, especially on automated cleaners or hoses
  • Excessive Chemical Consumption
  • Poor Water Quality
  • For ionization systems, difficulty in getting the copper level up to desired levels.
  • For chlorination, increase the amount of chlorine required to keep algae in check.


It is debated about the appropriate phosphate levels.  From my research it appears 50 ppb (Note-not 50ppm) or less is ideal.  You can maintain a pool with levels as high as 1,000 ppb, but it appears that more money is being spent on maintenance even at levels as low as 300 ppb.


There are many products available on the market to remove phosphates.  Phos-out and PhosFree are two popular products that have excellent feedback results.  For areas that are prone to phosphates, there is a weekly maintenance product called Pool Perfect by Natural Chemistry.  These products work by locking up the phosphates into a suspended solid that is filtered out by your filter. As the filter clogs with the suspended solid, backwashing sends the former phosphates into the street.


Regular pool maintenance:

The preventative measure of limiting phosphate exposure is taken by doing the following:


Remove leaves and organic material from the water as soon as possible

  • Vacuum and clean filters and pump baskets regularly
  • Be aware of the phosphate content of cleaners and chemicals used in and around the swimming pool
  • Don’t allow drainage from plants or the lawn to enter the pool