Phosphates may become an issue in your swimming pool as high levels of phosphates may promote the growth of algae.
While all water sources may contain phosphates and it’s not possible to completely eliminate phosphates you need to monitor the level of phosphate in your pool to ensure it’s not causing a problem.
Testing for phosphates is simple and easy with the right test kit or chemical test strips. As phosphates accumulate slowly over time you should only need to test every six months or at the start and end of the swim season.
If your phosphate level is too high you can reduce it with chemicals or simply drain some water from your pool and refill.
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What is Phosphate?
Phosphates are the naturally occurring chemical compounds containing the fundamental element phosphorus.
The application you will be most familiar with is fertilizer used on farms and your garden. Fertilizers feed the root system of plants promoting rapid growth.
Other applications of phosphates include personal care products, pharmaceuticals, industrial cleaners and fire extinguishers.
What Causes Phosphates in Your Pool?
Phosphates naturally occur in nature. Any biomass such as insects, flowers, leaves, seeds, skin, hair and other organic material will contain phosphates. When organic matter decays in your pool the water absorbs some of those phosphates.
Your local town water supply usually contains small concentrations of phosphates. If you are using an alternative source of water such as a dam, stream or well the phosphate levels may be significantly higher. Even rainwater may contain some phosphates.
Pool chemicals such as scale & stain removers and metal sequestrants contain phosphates.
Therefore, it’s not possible to completely eliminate phosphates from a pool but you will want to monitor the concentration to ensure it is not too high.
Why Test for Phosphates in Your Pool?
High phosphate levels are an indication of excessive organic material in your pool water. This is often the primary cause of algae growth, as algae is a water plant that loves to thrive on phosphate. Once algae begin to grow in your pool it will attract all sorts of unwanted guests, such as water bugs, frogs, etc., that want to feed on the algae and each other.
However, high levels of phosphates are not the only reason algae takes up residence in your pool. Inadequate chlorine sanitation, poor filtration and stagnant water will also promote algae growth.
Most phosphate test kits measure the concentration of orthophosphates which are the main nutrients for algae growth.
You need to prevent increased phosphate levels to eliminate algae breakouts and maintain clean, healthy pool water.
How to Test for Phosphates in a Pool
How do you test for phosphates?
Common pool test kits and chemical strips don’t test for phosphates. However, you can purchase pool phosphate test kits and strips which are inexpensive. If it’s convenient you can take a water sample to a pool shop and ask for a phosphate test.
Phosphates accumulate slowly in swimming pools so you will only need to test for phosphates every 6 months. I recommend testing at the beginning and end of the swimming season.
Most test kits or strips measure phosphate from 0 to 1000ppb.
[ppb is parts per billion, ppm is parts per million. 1000 ppb = 1 ppm.]
Ideally the concentration of phosphates in a pool should be below 250ppb (0.25ppm).
However, the concentration would need to be above 1000ppb (1ppm) to contribute towards significant algae growth. An unclean pool is more likely to be the cause of an algae breakout.
How to Lower Phosphates in Your Pool
The Chemical Option
Some pool owners add a phosphate reducer chemical to their pool to decrease the phosphate level.
I never recommend adding chemicals to eliminate other chemicals as you are only chemically polluting your pool. And remember, the less exposure you have to any chemicals the better for your health.
However, if you want to add phosphate reducer only use it if you have an excessive high level, like over 1000ppb.
Note: Phosphate remover is toxic in higher concentrations and known to cause cancer.
Don’t use a phosphate remover if you are using a metal sequestrant in your pool. Most metal sequestrants contain phosphate and the phosphate remover will reduce the effectiveness of the sequestrant. Now you have wasted your money twice.
The Natural Option
The best way to reduce the level of phosphates in your pool is to drain out some water and refill the pool.
Read our article on How to Drain a Pool
However, you always need to test your water source before taking up this option. If your water source contains phosphates, you may make the problem worse. Water from dams, rivers, bores or wells may contain much more phosphate than tap water.
One added benefit of partially draining and refilling your pool is you will lower the Total Dissolved Solids (TDS) in the pool.
Please read more on Total Dissolved Solids in Your Pool.
Pool Maintenance
When you have high levels of phosphates in the pool this is not the only reason algae takes up residence in your pool. Algae like dirty, stagnant water. If your chlorine sanitation and filtration is inadequate it will promote the growth of algae.
Regularly brush the pool to eliminate algae from clinging to the surfaces. When algae are floating around the pool they can be sucked into the pool cleaner or skimmer box.
Use a pool skimmer basket filter to capture all organic material before it reaches the filter. You need to clean the skimmer basket regularly so why not add a filter sock over the basket to capture more dirt and algae. This helps keep your filter cleaner longer and reduces stress on the filtration system.
Make sure you keep the filter clean and replace the filter element when it is worn.
When the pool water is balanced and clean add algaecide to the water to prevent algae from growing in the first instance.
Keep the pool covered when not in use to prevent algae spores entering the water.
Maintain your pool chemistry and chlorine levels within the recommended ranges.
Operate your pump for at least 8 hours per day during summer to ensure adequate filtration and circulation of water. You must filter all the pool water once every day.
And lastly, regularly shocking your pool will also prevent algae blooms.
Conclusion
I would not get overly concerned with phosphate levels in your pool unless they are above 300ppb (0.30ppm). Try not to add chemicals to solve the problem but rather empty some water from your pool and refill it. Swimming pools should be emptied every 5 to 10 years to solve the issue of accumulated total dissolved solids in the water. Emptying water also eliminates phosphates.
Keeping your pool and filtration system clean and in good order is the best way to prevent any issue developing with your pool water chemistry or sanitation.