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How to Lower Cyanuric Acid in a Pool – Effective Methods

Excessively high cyanuric acid (CYA) levels in your pool can stop chlorine from working effectively. To reduce high CYA, first test the cyanuric acid, drain the pool up to one-third of the way, refill the pool water, then test the CYA level again to see if you need to drain it further.

Cyanuric acid acts as a stabilizer for chlorine, but excessive levels can cause chlorine to become less effective in killing bacteria and sanitizing the water. Experts advise that if the CYA level in your pool is high, it’s only a matter of time till you notice reduced water quality. A Public Health Issues of Recreational Waters test also revealed that high CYA levels cause an increased risk of waterborne illness and the need for higher chlorine doses.

Draining the pool is one of the most common approaches for solving high CYA in pools. One of the first things I learned to prioritize during my internship as a technician at a pool cleaning service here in Arizona is that each time I drain a pool for high CYA levels, I have to rinse down the entire collection and give it a chlorine bath. Still, I do an acid wash if the CYA is about 200 ppm.

Now, suppose you’re a new pool owner. In that case, you’re probably only interested in a straightforward way to lower high CYA and how to go about it without consulting a pool service company.

In this article, I’ll explain why your pool’s CYA shouldn’t be too high and how you can correct it when it gets too high. I will also provide a few tips I learned as a pool technician that will help you reduce cyanuric acid without draining the pool – using a new, non-toxic chemical.

How to Lower Cyanuric Acid in a Pool

Lowering cyanuric acid in a pool is a practical solution to mitigate the dangers of high CYA levels. The most effective way is dilution, such as partially draining and refilling the pool with fresh water. But there are other intricacies for every step of the procedure. Here’s how to go about it:

Step 1: Test Your Pool’s Cyanuric Acid Levels

The right time to consider reducing your pool’s CYA level is between 40- to 80 ppm. The ideal level for CYA is 30-50 ppm., though some experts recommend letting the CYA get up to 95 before draining the pool.

But the point is that too much cyanuric acid ruins the chlorine in the water. 

You can test the cyanuric acid with test strips or liquid drops. Some pool stores will test for CYA with test strips, but only a few mobile pool services do both.

Here are the pros and cons of using strips vs. using drops:

  • Cyanuric acid test strips are quick but can be challenging to read. The colors vary from bright yellow to pink. Unfortunately, most CYA test strips don’t show anything over 100 ppm. Your pool could have a 300ppm CYA reading, but you wouldn’t know if you used the test strips. Nevertheless, they’re budget-friendly and easy to use.
  • Cyanuric acid liquid drop tests are much more accurate than strips. Most CYA liquid drops come in multipacks with multiple tests. They’re more accurate and don’t expire quickly. They provide higher readings.

The Taylor Swimming Pool Test Kit includes everything you need to test your swimming pool, including a cyanuric acid tester.

It includes a helpful chart that tells you when you need to add cyanuric acid or if you need to drain the pool to reduce the levels. I’ll show you another solution that doesn’t require draining later in the post.

Step 2: Drain the Pool ⅓ of the Way To The Bottom

Draining your pool’s stabilizer is the most effective way to reduce high CYA levels.

Some people can get away with only draining a foot or so in their pool. On the other hand, you might need to drain it multiple times to achieve the desired results.

Pro-tip: You should never drain a swimming pool more than one-third. If you drain it more than that, you risk damaging the liner permanently.

To drain your swimming pool, follow these steps:

  1. Turn off the pump to prevent it from sucking air into the system.
  2. Place a sump pump into the swimming pool.
  3. Plug the sump pump into the closest electrical outlet and attach a hose to the other end.
  4. Place the hose wherever you want the water to drain. Contact your city to know where to drain the water since pools often contain thousands of gallons.

If you need a sump pump, I strongly recommend the Superior Pump Pool Sump Pump because it includes a 10-foot cable and a powerful ¼-HP motor. You can use it to drain several thousands of gallons per hour, and it won’t crack or tear your pool’s liner or gunite. You can choose a variant with a bigger motor if you need to.

Protip: Keep an eye on the pool while draining. Too much water loss can cause damage to vinyl, gunite, plaster, and pebbles in your collection. I recommend emptying one foot at a time. Drain a foot of water, refill it, test the CYA levels, and repeat the process.

Step 3: Refill the Pool With Fresh Water

To refill the pool, pour hose water into the pool until the water is above the skimmer basket.

Don’t turn on the pump until the water exceeds the highest inlet. Remember to prime your pump when the pool is full. You should also open the filter’s air relief valve to eliminate excess air bubbles while the pump is running.

Pro-tip: I suggest avoiding this process during droughts and water shortages since you’ll likely require at least 2,000 gallons of water.

Step 4: Retest the Cyanuric Acid Levels in the Pool

When done refilling the swimming pool, it’s time to recheck the CYA levels. You’ll likely have to drain it multiple times if there is a ton of cyanuric acid in the water. For example, a CYA reading of 150 will drop to 100 after draining the pool ⅓ of the way, which is still above the recommended range.

Another suggestion is to remove the pool cover and let the sun’s heat evaporate the water. When you add hose water to the pool, it’ll dilute the cyanuric acid.

This method takes much longer than draining, but it’s the way some pool owners maintain the CYA levels without knowing it. Rainwater can also naturally dilute the stabilizer, so you might consider leaving the cover off when it rains.

How Do I Lower the Cyanuric Acid In My Pool Without Draining It?

To lower the cyanuric acid in your pool without draining it, follow this process:

  1. Test the water and keep the chemicals within their optimal rangesAccording to the United States federal health agency, the Centers for Disease Control and Prevention (CDC), chlorine should be between 1 and 5 ppm, pH between 7.2 and 7.8, and alkalinity between 80 and 120. If any of these ranges deviate, this process won’t work, and you’ll have to drain and refill the pool.
  2. Pour Bio-Active Pool Stabilizer Reducer into the skimmer after removing the basket. Turn on the pump and allow it to run as much as possible throughout the following week. This cyanuric acid reducer needs constant circulation to work, as it has to come into contact with as much water as possible.
  3. During treatment, don’t use chemicals other than chlorine, soda ash, muriatic acid, and baking soda. Most other pool chemicals disrupt the process. Bio-Active is extremely sensitive, so your pool must work correctly within the recommended parameters.
  4. Keep the swimming pool above 65 degrees Fahrenheit (18.3 Celsius). Bio-Active CYA Reducer uses natural ingredients that don’t work in cold water. Learn how pools are heated to ensure the water never dips below the required temperature.
  5. Remove algae blooms and cloudiness as quickly as possible. Algae can interfere with the stabilizer reduction process. Too much algae, total dissolved solids, and other debris will make it impossible to see results.

This method takes about 7 to 10 days. Bio-Active is selective, as the manufacturer recommends it only for pools with an acid level of 3 to 330 ppm, but using it is the only way to reduce the cyanuric acid without draining the water. It can drop the CYA by up to 50%, returning it to the recommended range between 40 and 80.

Note: If your pool has extremely high cyanuric acid levels, you’ll likely have to use two or three bags of Bio-Active. For example, a CYA reading of 300 will drop to 150 after one sack and 75 after two bags.

If you want to learn more about using Bio-Active to lower stabilizer in a pool, watch this Leslie’s Pool Supplies video on YouTube:

How Risky Is a High Level Of Cyanuric Acid In A Pool?

According to pool maintenance expert Joe Trusty, the primary risk of excessively high levels of cyanuric acid is that it leads to reduced chlorine effectiveness, potentially allowing harmful bacteria and pathogens to thrive in your pool.

But beyond that, high levels of CYA can cause cloudiness in the water and hinder the pool’s overall sanitation.

Portage County Combined General Health District (PCHD) advises that “CYA Levels exceeding a threshold of 70 ppm of cyanuric acid can reduce the effectiveness of the chlorine in a pool.”

On the other hand, the amount of time it takes to kill bacteria lengthens as the concentration of CYA increases. According to PCHD, the ideal level for CYA in your pool is between 30 to 50 ppm.

What Causes Cyanuric Acid to Be High in a Pool?

Cyanuric acid is high in a pool when too many chlorine tablets, too much pool conditioner, or stabilizer-packed chemicals are added to the collection. Your pool’s CYA shouldn’t exceed 100 ppm since, according to a leading manufacturer of water quality testing products, LaMotte, it’s too high to let the chlorine work. It’ll prevent chlorine evaporation, but the chlorine won’t be able to sanitize the water.

Your pool’s chlorine will be effective when the cyanuric acid reaches 90 ppm, but 100 ppm renders it useless. A few things contribute to high CYA levels, which you can monitor and maintain.

Here’s what increases the cyanuric acid in your pool:

  • Most chlorine tablets contain cyanuric acid: Look for a label that mentions chlorine stabilizer, CYA, or pool conditioner. All these terms mean the same thing: there’s a lot of cyanuric acid in the tablets. The CYA in the tablets passively increases the levels to a healthy range, but a lack of dilution can elevate the CYA too much.
  • The pool conditioner increases the swimming pool’s cyanuric acid: You can buy conditioner in liquid or granular form. Don’t add too much CYA to the collection simultaneously, or you’ll quickly exceed the recommended range. I suggest getting the CYA to 40 and letting the chlorine tablets do the rest.
  • Some other pool chemicals contain trace amounts of cyanuric acid: Check the ingredients of anything in the water to ensure no stabilizer. If there is, it will likely increase your pool’s cyanuric acid. While CYA is essential for all swimming pools, you should not add it to everything you dump into the water.

Pool owners often overcompensate for the lack of chlorine activity by pouring more shock or liquid chlorine into the pool.

You can add loads of chlorine into the water without it doing anything other than creating a hazardous swimming environment. Therefore, you should lower chlorine levels from 1ppm to 5ppm when swimming or using CYA reducers.

Is It Safe To Swim in a Pool With High Cyanuric Acid?

Swimming in a pool with high cyanuric acid is safe, but it can be mildly irritating to the eyes. Diluted cyanuric acid doesn’t cause itchiness or irritation, so you likely won’t feel anything. However, too much CYA can render your chlorine useless.

Keep these things in mind before swimming in a pool with high cyanuric acid:

  • Most cyanuric acid treatments recommend waiting 20 minutes before swimming. Test the pool once the liquid or powder solution dissolves to know if you have high CYA. The reading will always be much higher if you test a concentrated portion of cyanuric acid in the swimming pool.
  • Know how to backwash your filter after using a cyanuric acid reducer or increaser. Both treatments can get trapped in the filter, and you must remove them. Backwashing the filter removes the excess cyanuric acid, freeing your chlorine to be much more effective.
  • Too much cyanuric acid in the pool can cause algae blooms because it limits chlorine’s potency. While CYA might not directly harm your health, a report featuring experts on HealthNews, a provider of emerging research, new treatments, diet, and exercise, revealed that the algae floating in the water and stuck in the porous liner could be dangerous. Clear up all algae blooms and cloudiness before swimming in the water.
  • Cyanuric acid can lower the pool’s pH and alkalinity, making it dangerous for swimming. Test the pool’s pH, alkalinity, and chlorine before entering the water. Remember to use soda ash and baking soda to increase the pH and alkalinity. 

Cyanuric acid isn’t directly dangerous to swim in when it’s diluted in a pool. However, it can cause multiple unwanted side effects, leading to unsettling, hazard-ridden swimming pools.

Always check and maintain your pool’s CYA before taking a dip. While you’re here, you can check out my recent article, where I’ve explained in detail how to lower the pH and alkalinity in your pool.


How do I lower cyanuric acid in my pool?

The practical solution to lowering cyanuric acid levels in your pool includes testing the cyanuric acid levels using a pool test kit, then partially draining your pool to dilute the cyanuric acid. After that, you refill the pool with fresh water.

Remember to retest the cyanuric acid levels, repeat the process if necessary, and regularly monitor and maintain proper cyanuric acid levels for optimal pool chemistry.

What are the dangers of high cyanuric acid levels?

Cyanuric acid is a stabilizer for chlorine in pools, but excessive levels can reduce the effectiveness of chlorine, leading to inadequate sanitization. This can result in harmful bacteria and algae growth, increasing the risk of waterborne illnesses. 

High cyanuric acid levels can cause cloudy water, skin, and eye irritation and potentially damage pool equipment over time.

How do I test for cyanuric acid levels?

You can use a cyanuric acid test kit to test for cyanuric acid levels in a pool or spa. First, collect a water sample from the pool or spa, then add reagents to the water sample and observe the color changes. Compare the color of the model to the provided color chart to determine the cyanuric acid level.


  • Raoul Hayes

    Raoul Lobo is a seasoned expert in the realm of home appliances and environmental comfort. As a prominent author at, Raoul's passion and expertise shine through in his insightful articles and guides. With years of hands-on experience, he has become a trusted source for readers seeking advice on pools, washers, dryers, and a wide range of other appliances.

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