How to Test For Phosphates In Your Pool Water

Written by Michael Dean
May 18, 2023

testing for phosphates in swimming pool water

Testing, balancing, and adjusting chemicals is one of the most important pool maintenance tasks. To stay on top of algae infestations, monitoring and testing for phosphates in your pool water is crucial. Phosphates are pesky nutrients that contribute to algae growth.

In this article, I’ll cover everything you need to know about testing for phosphates, go over the recommended phosphate levels, and walk you through how to remove them from your swimming pool.

Main Takeaways

  • You can test for phosphates in your pool using test strips or liquid test kits. Alternatively, you can get your water professionally tested.
  • Normal phosphate levels in a swimming pool range between 50 to 125 parts per billion (ppb).
  • Phosphates can enter the pool through fertilizer runoff, debris and organic matter, swimmers, and rainwater.
  • If left untreated, phosphates can pave the way for algae to thrive and grow in your pool.

How To Test For Phosphates In Your Pool

There are a few different ways to test for phosphates in your pool. Let’s go over each method.

Pool Test Strips

Usually, the most widely-available pool test strips are designed to measure just the basics: pH, chlorine, alkalinity, and cyanuric acid levels. However, some test strips can also measure phosphate levels in the water.

To use it, dip the test strip into the pool water and remove it from the water after a few seconds. Then give the strip a little shake to remove the excess water. Finally, compare the color on the strip with the color chart provided with the test strip to determine the level of phosphates in your pool. Make sure to follow the manufacturer’s instructions and check the expiration date before use.

Liquid Test Kits

You can also use liquid test kits to test for phosphates in pool water. These kits usually come with a test tube, reagent, and color chart.

To use a liquid test kit, fill the test tube with pool water, add the correct number of reagent drops, and then compare the resulting color of the water with the color chart.

I have more tips on DIY pool water testing in my complete article on the topic, linked here.

Professional Testing

If you’re unsure how to test for phosphates in your pool and want to ensure you get an accurate reading, you can also have your pool water tested by your local pool store. Just bring a sample of your pool water the next time you’re in the store, and they will be able to test your water for you. They can give you a comprehensive analysis of your pool water, including phosphate levels, and recommend any necessary treatments to balance your pool water chemistry.

What Are Normal Phosphate Levels?

Ideally, you will have no phosphates in your water, but anything below 100 to 125 parts per billion (ppb) is acceptable. But with that said, try and aim to maintain a lower phosphate level below 100 ppb to stop algae from gaining a foothold in your water.

If the phosphate level in your pool is higher than 300 ppb, your pool is at a higher risk of an algae bloom, which can turn your pool water green and cloudy. If the test shows you levels above 500 ppb, the situation is dire, and you need to address it immediately!

Why Is It Important To Test For Phosphates?

The primary issue with high phosphate levels in pool water is that it can contribute to algae growth. With algae thriving in the presence of phosphates, it can quickly spread throughout the pool, making it unsightly and unsafe for swimming. Algae blooms create a toxic swimming environment and can be a serious health hazard.

Furthermore, high phosphate levels can also make it difficult to maintain proper water chemistry in a pool. Phosphates can interfere with the effectiveness of chlorine, making it harder to keep the water clean and clear. This can lead to increased chemical use and costs associated with maintaining the pool.

The role phosphates play in fostering algae growth while suppressing the effectiveness of chlorine makes it pretty important to test for it on at least a monthly basis.

Where Do Phosphates Come From?

Phosphates can come from both natural and man-made sources. Understanding where they come from is the first step to preventing them from entering your pool water in the first place.

Fertilizer Runoff

One of the most common sources of phosphates in pool water is fertilizers. Fertilizers contain high levels of phosphorous, which can easily leach into the soil and spill over into your pool. Avoid using fertilizers in planter boxes or other landscaping near your pool.

Debris and Organic Matter

Phosphates can also enter your pool through debris and organic matter, such as leaves, grass clippings, and insects. These can contain high levels of phosphates, which can enter your pool water as they decompose. To prevent phosphates from organic matter, skim and clean your pool regularly and remove all debris immediately.


Swimmers can also introduce phosphates into a pool through sweat, skin cells, bodily oils, or bodily fluids.

Furthermore, swimmers can bring in other contaminants, such as sunscreen, cosmetics, and hair products. These contaminants can easily enter the water and contribute to the overall phosphate level.

To prevent swimmers from contributing to the buildup of phosphates, encourage good hygiene practices among swimmers. This includes showering before entering the pool, using the restroom before swimming, and avoiding using cosmetics and hair products in the water.


A sudden storm is a way in for all kinds of uninvited microorganisms. Rainwater can carry a range of contaminants, including phosphates, from the atmosphere and surrounding environment. If your pool is exposed to frequent rainfall, test for phosphates regularly and take steps to prevent them from entering your pool water.

Pool Chemicals

In addition to these sources, phosphates can also be found in some pool chemicals, such as algaecides and clarifiers. While these chemicals can help maintain proper water chemistry, use them in moderation and follow the manufacturer’s instructions to prevent overuse and the buildup of phosphates in your pool.

How To Remove Phosphates From Your Pool

The easiest method to remove phosphates from your pool is to use a phosphate remover. These products bind to the phosphates in the water, making them easier to filter out. Several types of phosphate removers are available, including liquid and granular formulas. Make sure to follow the manufacturer’s instructions carefully when using these products, and don’t use too much.

While using a phosphate remover removes the phosphate itself, this is only part of the solution. Once you’ve eradicated the phosphates, you must shock your pool to kill off any budding algae spores, rebalance your pool chemistry, and circulate and filter your water over the next few days to address the problem from all angles. Keep monitoring your water and testing it for phosphates as well as other pool chemicals.

Do You Really Need Phosphate Remover?

If your phosphate levels are above 300 ppb, using a phosphate remover may be useful. But if phosphate levels are within the normal range (less than 100 or 125 ppb), you won’t need to use a phosphate remover, as the levels are not high enough to cause significant problems. 

Another point to note is that phosphate removers are not environmentally friendly. Lanthanum, an active ingredient used in phosphate removers, is moderately toxic to the environment.

Thankfully, there are better alternatives to using a phosphate remover. More on this below.

Alternatives To Phosphate Remover

In the event of a phosphate problem, try the following instead of using a remover.

Filter Aggressively

Turn your pool pump and filter on high for a few hours to clean your water out while you work on sanitizing the water. If this is ineffective, backwash and clean your filter before trying again. Phosphates can accumulate in your pool filter over time, so backwashing your filter regularly can help remove them from the water.

Drain And Refill The Pool

If phosphate levels are extremely high and other methods have been unsuccessful in reducing them, you can drain and refill the pool as a last resort. This should be done carefully and under local regulations to avoid water waste and potential damage to the pool structure. If you have any doubts during the process, call a professional.

Get My Free Pool Care Checklist

Download my free, printable pool maintenance checklist to help you accomplish regular pool care tasks for any type of swimming pool.

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How To Keep Your Phosphate Levels Under Control

Here are my top tips to help you keep your phosphate levels under control and prevent them from becoming too high:

  • Test your pool water regularly to monitor phosphate levels.
  • Regularly clean your pool and remove debris such as leaves and grass clippings to reduce the amount of organic matter and phosphates in the water.
  • Read the bottle before using algaecides, clarifies, and other chemical treatments, as these chemicals may contain phosphates.
  • Cover your pool when not in use to prevent debris and other organic matter from entering the water and contributing to high phosphate levels.

Well, that’s it for testing for phosphates. Don’t hesitate to reach out if you have any more questions.

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