Phosphate Contamination in Pools

drpoolPhosphates became something of a dirty word in the 70’s – when environmental scientists put some blame on the eutrophication (nutrient enrichment) of rivers and lakes with phosphates used in laundry detergents.

In the late 90’s pool chemical manufacturers began marketing phosphate removers, as a way to combat growing levels of phosphates in pools, and remove a primary food source of algae.

Types of Phosphates in Pools

phosphate-compoundPhosphates can exist in many different forms in a swimming pool. It can enter the pool as a polyphosphate, or phosphate compound, from many sources (see below). These compounds will eventually convert to an orthophosphate, the type of phosphate that fuels algae growth. Further combination with high levels of calcium in the pool can create a calcium phosphate, which can lead to scaling problems.

Sources of Phosphates in Pools

There are many sources of phosphate contamination in pools – some you can control, some you cannot. Phosphates constantly enter the pool.

  • Decaying plant matter – any organic debris in the pool, even algae!
  • Soil Contamination – flooding, mudslides, overflowing mulch beds.
  • Contaminated Fill Water – even city water can contain phosphates.
  • Bather Waste – Urine, sweat, fecal matter, skin cells, cosmetics.
  • Lawn and Plant Fertilizers – can blow in, wash in, or track in the pool.
  • Agricultural or Construction Dust – blown into pool, washes off trees.
  • Birds, Dogs, Ducks – body wastes, dirt and excrement in the pool.
  • Soap, Shampoo and Detergents – most contain polyphosphates.
  • Some Stain & Scale products – those containing HEDP phosphates.

stain-awayDid you see that last one? It’s true – many sequestrants used to control metals and minerals from staining and scaling, actually add phosphates to the pool! Our own Stain Away contains Diphosphonic Acid, (a powerful sequestering agent) which can degrade to Orthophosphates when conditions are right.Natural Chemistry's Metal Free

If you use stain & scale control in your swimming pool (a good idea), but also have a problem with phosphates building up – my suggestion is to use Natural Chemistry’s Metal Free and/or Scale Free, which are made without HEDP, and will not contribute to phosphate levels.

Testing for Phosphates in Pools

When phosphate removers were first brought to market, they were difficult to use correctly, being that there was no method for testing for phosphates outside of a laboratory.

That all changed a few years ago, with the development of a 1-minute phosphate test for home use. It’s slightly more involved than a regular pool test strip, but will yield results in less than a minute.phosphate-test strips

Phosphate test strips measure the level of Orthophosphates, or PO4, in the pool water. A level of 500 ppb (parts per Billion) in the water could be enough to trigger an algae bloom.

Phosphate Removal in Pools

Phosphate removers are made by SeaKlear and Natural Chemistry in many formulations – some combined with clarifiers or enzymes.

seaklear-phosphate-removersPhosphate removal chemicals are commonly derived from salts of lanthanum. These positively charged ions are strongly attracted to the negatively charged phosphates. Once combined, the weight of the compound knocks it out of solution, where the salts settle on the floor, or become trapped in your pool filter.

phosflocFor extremely high levels of phosphates in the pool, use PhosFloc, to quickly precipitate phosphate levels of 2500 ppb, or more. A flocculent will drop suspended particles to the pool floor. When the water is clear, vacuum the pool to waste, to remove the salts from the pool.

If you’ve battled algae in your swimming pool every year, and it seems to be getting worse, you may have a phosphate contamination. Have your water tested for phosphates, or use our inexpensive test strips to determine the level of contamination.

One more thing – phosphate removers won’t kill algae, they only remove a primary food source for algae. Kill the algae with pool shock or another powerful algaecide – and to prevent repetitive algae blooms, use a phosphate remover to literally ‘starve algae into submission’.

Class dismissed!


Dr. Pool

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