Phosphates in Pools

Phosphates will always be present in your swimming pool water. However only in excess will phosphates affect your water. Excessive phosphates will lead to algal blooms and will turn your pool water green.

Article published on Palintest website – 13/05/2019


Phosphorus is essential to life and is described as a macronutrient. Phosphorus exists in water as the phosphate ion (PO43-). Phosphates come from rocks, so the sources are finite and non-renewable. Phosphorus is used in fertilizer and so enters the ground and surface water through surface soil runoff.

How does phosphate enter your pool water?

There is a common misconception that phosphates are only introduced to a pool from rainfall. Although rainwater may affect your pool water as it contributes to surface run off, the biggest source of phosphates in pool water is the bather. Phosphates are found in many lotions, shampoos, and make up products, in addition to soil and leaves.

Phosphates are introduced to the water by any of the following:

  • From rainfall, sprinkler systems or surface run-off washing into the pool.
  • From garden fertilizers being washed into the pool.
  • Wind blowing dirt, leaves, twigs back into the pool.
  • Addition of fresh water to the pool as mains water has some phosphate present.
  • The use of pool chemicals containing TSP in and around the pool.
  • Bathers with cosmetic products on their skin entering the pool.

What does phosphate do to your pool water?
High phosphate levels provide nutrients for algae to grow. When orthophosphate levels (simplest form of phosphates which are consumed by algae) are too high, algae will become resistant to disinfectants, even when shocking the pool, and an algal bloom will occur.

The presence of high level of phosphates and hence algae will result in the following:

  • Poor water chemistry.
  • Cloudy green water.
  • Green and mustard colour debris.
  • Slimy and slippery surfaces.
  • Excessive chemical use.

Be proactive!
Phosphates are inevitably in your pool water, but you can do the following things to limit the amount of phosphates:

  1. Remove leaves and other organic material from the water as soon as possible.
  2. Clean filters and pump baskets regularly.
  3. Regularly vacuum bottom of the pool.
  4. Be aware of using chemicals containing phosphates in and around the pool.
  5. Prevent drainage water from the surroundings from entering the pool.

These steps will ensure that you maintain low levels of phosphate!

To keep algae bloom at bay, we suggest the following:

      • Maintaining adequate disinfection levels.
      • Maintain adequate pH levels.
      • Regular phosphate testing.
      • Adequate filtration.
      • Routine backwashing.

When deciding your frequency of testing, remember to take the following into consideration: Bather load, Outdoor or Indoor poo, Source water levels of phosphate.

Protect your bathers!

  • Regular testing for phosphates is key to ensuring your pool is kept clean and blue. Phosphate testing can use either visual or digital technologies: Pocket Kit / Contour Comparator / Photometer.
  • The Palintest latest photometer the Pooltest 10 now has the additional benefit of phosphate testing and covers all key pool water parameters, in an accurate, quick and precise manner.

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