How to test for phosphates in a pool - Sutro, Inc

How to test for phosphates in a pool

Phosphates are a common and integral element of our natural ecosystem, which is why you also find them in your swimming pool. 

They can sometimes be crucial to maintaining your pool water. Let’s learn about the importance of phosphates in a swimming pool and how to test and remove them. 

Where do phosphates come from?

Phosphates are naturally occurring compounds made from a combination of phosphorus and oxygen. These can be organic or inorganic in nature and can get into the pool from various sources. Here’s a list to name a few:

  • Bather Load: People using the swimming pool can contribute phosphates through sweat, body lotions, soap, or detergents used to clean towels/swimwear.

  • Organic Matter: Things like twigs, dry leaves, insects, or other microorganisms can contribute to the phosphate levels in the pool.

  • Water Runoff: Garden care products, fertilizers, or other chemicals used around the pool can seep into the pool water and add phosphates.

  • Water Supply: In recent years, municipal water supply has seen a significant increase in phosphate levels due to the excessive use of phosphates in water treatment plants. 

Why should you monitor phosphates level? 

Phosphates are the leading food source of algae in the water. So high phosphate levels can promote algae growth, causing the water to turn green/cloudy.

High levels of phosphate in the pool will increase the algae growth, which will lead to faster depletion of the sanitizer (chlorine). This results in inadequate chlorine levels requiring frequent addition of chlorine and making maintenance more time-consuming. 

On the positive side, phosphates bind with calcium and other minerals, which can help soften the pool water. Phosphates alone are not a big problem, but combining high phosphate levels with water chemistry imbalance can wreak havoc on the pool. 

How can you test the phosphate in your pool?

Most people usually avoid testing phosphates due to their irrelevance under ordinary circumstances. This is why most pool testing kits, test strips, or digital pool monitors do not test for phosphates. There are two methods of doing this:

  • Take a sample of your pool water to your local pool store and ask them to check it for phosphates. It is also an excellent opportunity to conduct a detailed pool water check.

  • Use a phosphate pool test kit. These kits are specially designed to test phosphates and are very accurate. 

How to get rid of phosphates? 

If the levels of phosphates in your pool water have exceeded 500 ppb (parts per billion), it is time to take action.

Additionally, if the recurrence of algae in your pool water is very frequent, it may also indicate high phosphate levels.

  • Use a phosphate remover chemical in the pool water. Refer to the instructions on the packaging label for the exact quantity and procedure.

  • Monitor your pool water for balance, and maintain proper chlorine levels. 

The best remedy is to constantly monitor the water chemistry of your pool. Our Sutro Pool Monitor makes this task easy as it automatically checks the sanitizer, pH, and alkalinity levels in the water thrice-a-day. So, Sutro will promptly alert you when the sanitizer levels start falling below normal and opens the door for algae to start feeding on phosphates. 


Do phosphates affect chlorine?

Although phosphates do not react directly with chlorine in a pool, high levels of phosphates promote algae growth, so more chlorine is used to keep the water sanitized. 

Can you swim in a pool with high phosphates?

Yes, you can swim in a pool with high levels of phosphates without any direct impact on your health. However, the water should have adequate sanitizer (chlorine), pH, and alkalinity.

Can you have high phosphate but no algae in the pool?

Yes, it is possible to have high phosphate levels but no algae if you maintain proper chlorine levels and regularly use an algaecide. Algae feed on phosphates, but regular use of sanitizer and algaecide,will keep a check on the phosphate levels.

Back to blog