High Phosphate Levels

High Phosphate Levels In Pool - How To Fix It?

Phosphates are one of many dissolved compounds that can be present in pool water. Although phosphates are not a concern for many pool owners, occasionally, high phosphate levels can lead to difficulties controlling algae.

In this article we will discuss the causes of high phosphate levels, how to identify them, and what problems they can cause in your pool. We will also cover how to lower phosphates, and how to prevent them from rising again in the future.

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What Causes High Phosphate Levels?

High phosphate levels have a few different causes. In most cases, phosphates are being introduced to your pool through normal use, but there are some exceptions.

Before attempting to diagnose a high-phosphate problem, you may want to check the source water for your pool. Some public-owned water supplies may have phosphates added in order to reduce trace metals in drinking water. Test the water you fill your pool with to find out if high levels of phosphates are already present at your tap.

Phosphates can also be introduced to the pool through organic debris, such as leaves and lawn trimmings. Phosphates are naturally released by organic matter as it begins to decay.

Garden runoff can also contribute to your high phosphate levels. Most garden fertilisers contain phosphate as a plant nutrient, and during a heavy rain, traces of these phosphates may end up in your pool water.

Swimmers also introduce phosphates to your water. These are sometimes introduced through organic compounds such as skin cells and hair, but can also enter your pool from laundry detergent, skincare, or hair care products.

However, the main way that swimmers introduce phosphorus into your pool is via urination. Urine contains around 1,800 mg/L of phosphate (1,800 ppm), which is huge compared to the levels required for an algae outbreak, as you will see shortly.

One final contributor to high phosphate levels is pool chemicals. Certain chemicals used as pool cleaners, stain removers, or stabilisers may have high concentrations of phosphates. Pool treatments are the most typical culprit for sudden onset levels of high phosphates.

Why High Phosphate Levels are a Problem for Your Pool

Having high phosphate levels is not dangerous for humans, and may not affect other aspects of your pool’s chemistry. However, when left unattended, high phosphates will feed colonies of unwanted microorganisms in your pool.

All types of algae feed on phosphates, including the difficult to remove black-spot algae, and blue green forms of algae that are capable of producing cyanotoxins.

Algae need a few different things to thrive in your pool (such as sunlight, carbon dioxide and nitrogen) but generally speaking, phosphates will be the first thing to run out and prevent them from growing further.

For this reason, scientists call phosphorus or phosphates a ‘limiting nutrient’. This means that while your algae situation might be stable now, a slight increase in phosphates can be enough to set them off and initiate a bloom.

Because phosphate is a vital nutrient for algae, keeping your phosphate levels in check is essential to preventing algae infestations.

Other microorganisms such as bacteria also feed on phosphates. Although bacteria is uncommon in pool water with adequate chlorination, high phosphates can increase the likelihood of bacterial colonies developing in neglected pools.

As algae infestations are also known to harbour these bacteria, keeping your phosphate levels in check is essential to keeping your pool both clean and safe to use.

How to Identify High Phosphate Levels in Your Pool

While algae growths and cloudy water can be signs of high phosphates, the only way to diagnose your phosphate levels accurately is by using a phosphate testing kit. We recommend the Insta Starver pack of phosphate test strips because it is easy to use and provides fast results.

There is some disagreement as to what levels of phosphate are high enough to be of concern, but the general consensus is that pools with phosphate levels above 500 ppb (parts per billion) are at an increased risk of algae and bacterial growth.

Note that we said parts per billion, not parts per million like we normally do when discussing pool water chemistry. There are 1,000 ppb in 1 ppm - this is why when someone urinates in your pool with a phosphate concentration of 1,500 ppm, it can have a substantial effect even when diluted amongst the entire pool volume.

If your pool’s levels are reading at less than 500 ppb, but greater than 300 ppb, this is a sign that phosphates may need to be addressed soon, but are not yet at a critical level. If algae is already present in your pool, it is recommended to keep a phosphate level lower than 300 ppb to help expedite the removal process.

How to Lower Phosphate Levels

In order to lower phosphate levels in your pool, you will need to use pool treatment chemicals known as phosphate removers. These contain chemicals that remove phosphates by binding to the molecules and causing them to change into a form that is less harmful for your pool.

For moderately high phosphate levels, we recommend a phosphate remover called Starver M. This remover does not require mixing or need to be vacuumed up after use, and also won’t cause pool water to become cloudy like other products.

When used in a pool of 50,000 litres, one dose of Starver M can remove up to 2 ppm (parts per million) of phosphates. This is equivalent to 2,000 ppb, and is enough to eradicate high phosphate problems in pools this size or smaller. This product’s intensity can be scaled down as needed, making it a great option for moderately high phosphate levels.

If you have very high phosphate levels and are getting readings of 2,000 ppb or more, you will need to use a stronger phosphate remover. Starver X is an extra-strength phosphate remover, great for removing phosphates from pools that have been in a state of disrepair for a while.

When used in a pool of 50,000 litres, one potent dose can remove up to 6,000 ppb of phosphates. This product is one of the most intense phosphate removers available, and is a wonderful option for those renovating old pools that may have been abandoned.

Occasionally, you will need to use a weaker phosphate remover, such as Starver M, on a regular basis to maintain lower phosphate levels after performing a more intense removal treatment.

This is usually only recommended for pools where the phosphate levels cannot be controlled through other methods, as some brands of phosphate removers contain chemicals that are known to be toxic in large quantities (ie. lanthanum chloride). The goal for most pool owners should be reducing the need to use phosphate removers.

Before using any phosphate removers, use this pool volume calculator to know how much water you're dealing with. This will help you calculate the appropriate dose for your pool.

How to Prevent Phosphate Levels From Rising in the Future

High phosphates do not have to be a repeat occurrence in your pool. We’ve created a list of steps you can take in order to prevent pool phosphates from accumulating above acceptable levels in the future.

Remove Organic Debris From Your Pool

Organic debris is one of the main causes of phosphate buildup in swimming pools. In order to prevent phosphates from rising, it’s important to remove organic debris as soon as it enters your pool, or to prevent it from entering in the first place.

We recommend running your skimmer and filter system for a minimum of 8 hours per day in order to reduce floating debris. If you have time available, using a hand-held net is also a great option for removing large amounts of debris that can accumulate during storms.

It is also important to use a vacuum to remove any debris that has settled out on the floor of your pool. If you have a pool with a large surface area, we recommend using an electric, cordless vacuum that can be hand-held or attached to the provided telescopic pole.

Stop Organic Debris From Entering Your Pool

Preventing additional debris from entering your pool can also keep high levels of phosphates from accumulating.

Asking swimmers to shower before entering your pool drastically cuts down on the amount of organic debris introduced through skin, hair, and sweat. Clean swimmers also introduce less skincare products to your pool, which can contribute to high phosphates as well as other chemical imbalances.

Removing plants near your pool is a great way to reduce the organic debris that creates high phosphates. Consider trimming, removing, or relocating any plants that are close enough to your pool to regularly drop leaves or twigs into the water.

It’s also important to prevent any garden runoff from areas where plant fertilisers are used, including the fertilisers that come pre-added to many potting soil mixes. Plants will often need to be relocated, but you may also want to consider adding landscaping elements that redirect the flow of garden rainwater away from your pool.

Get The Kids To Stop Urinating In Your Pool

As mentioned earlier, urine contains a large load of phosphates. If you can get the kids to go to the toilet before they swim, you can stop most of the phosphates before they ever make it to your pool.

However, this is easier said than done! No matter how clear you are about not weeing in the pool, they seem to hit the water and just lose complete control of their bladder…

If anyone has any good ideas here, I’m all ears!

Clean Pool Equipment Regularly

Organic debris can also hide in other areas of your pool, such as on skimmer baskets, in their housing units, or inside of your pump and filter. It’s important to clean your filter regularly with a soft-bristled brush and rinse it with clean water before reinserting it into your pump.

If you have had lots of debris in your pool recently, caused by something like a storm or an algae infestation, it might be a good idea to replace your pool’s filter. We recommend replacing your pool’s filter any time you cannot get it reasonably clean through manual effort.

Maintain Proper Pool Chemistry

Keeping your pool’s chemistry balanced can also decrease the chances of developing a high phosphate problem in your pool.

It’s especially important to regulate the amount of dissolved calcium in your pool because calcium interacts with phosphate particles. Keeping your calcium levels balanced will help prevent your phosphate levels from rising because calcium binds to free phosphates in your pool water.


Phosphates occur in most pool water and are not usually a problem unless they occur in very high amounts. In higher amounts, phosphates can fuel the growth of algae and other bacteria. Luckily, high phosphates levels are easy to diagnose and treat.

Do you have any questions about high phosphate levels in your pool? We’d love to hear from you in the comment section!

Louis from Pool Advisor


A chemical engineer by trade, Louis is committed to debunking myths in the pool industry by explaining the underlying chemistry and making it accessible to all.