How to Lower Cyanuric Acid Levels In Your Pool

Written by Michael Dean
December 27, 2023

lower cyanuric acid in swimming pool

Balancing water chemistry can often feel like a constant game of seesaw. It would be amazing if pool chemicals stayed the way they’re supposed to so you can jump into clear, clean water without worrying about pH or alkalinity. But it is up to pool owners to keep their swimming pools in tip-top shape. Maintaining proper water chemistry is one of the most valuable skills a pool owner can have. This is certainly the case when cyanuric acid levels in your water also jump up too high.

Keep reading to learn more about what causes high cyanuric acid levels in pools and how to lower those levels to ensure a safe and comfortable swimming environment. Whether you’re a pool owner or a frequent swimmer, it’s important to understand the role of cyanuric acid in pool maintenance and how to manage it properly.

Main Takeaways 

  • High cyanuric acid can be caused by too much chronic stabilizer, algaecides, or pool water supply from local municipalities already containing cyanuric acid.
  • Too much cyanuric acid can harm the chlorine effectiveness of your pool, cause inaccurate alkalinity readings, and lower your pH.
  • The two options for reducing cyanuric acid levels in your pool are a partial drain-and-refill or using a cyanuric acid reducer.

What Causes High Cyanuric Acid?

Cyanuric acid, or CYA, is a mild and odorless acid that forms a weak bond with the free chlorine in the pool water, protecting it from the sun’s UV rays. This reduces the loss of excess chlorine from the water during the daytime. When managed properly, cyanuric acid is a super beneficial chemical since it lessens the amount of chlorine you have to mix into your water. But there’s such a thing as too much of a good thing. Your water could have far more cyanuric acid than it needs. Here are some reasons why.

Overuse of Chlorine Stabilizer

One of the most common causes of high cyanuric acid levels in pools is the overuse of chlorine stabilizers. Chlorine stabilizer, also known as cyanuric acid, is added to pool water to protect chlorine from the sun’s UV rays, but too much of it can cause CYA levels to build up. Use my stabilizer calculator to ensure you add the right amount.


Some algaecides contain cyanuric acid as an ingredient, which can lead to a build-up of the chemical in the pool water if used excessively.

Stabilized Chlorine

Similarly, some types of chlorine (trichlor and dichlor) are stabilized, meaning they already contain CYA. A pound of trichlor in a 10,000-gallon pool can raise cyanuric acid levels by 6 ppm (parts per million). Read the labels for any pool chemicals you use carefully to ensure you’re not accidentally doubling-dosing your water.

Tap Water

Some municipalities add cyanuric acid to their water supply for swimming pools, which can contribute to high levels in a pool if the water is not properly tested and adjusted. This is easy to figure out; you could contact your local water supplier to ask them about the chemical makeup of their water or test a sample yourself to ascertain the cause.

Lack of Proper Pool Maintenance

Lack of regular pool maintenance and pool water testing can also lead to high cyanuric acid levels. By not keeping your pool and equipment in good condition, it’s hard to identify the cause of your issue and take appropriate actions to correct it. When in doubt, call a professional for help.

What Happens If Your Cyanuric Acid Levels Are Too High?

The ideal level for CYA is 30-50 ppm. Anything below or above that, and you’ll encounter several issues.

Interference with Chlorine Effectiveness

High levels of cyanuric acid can hurt the effectiveness of chlorine in killing bacteria and other contaminants in the pool water, making the water more susceptible to contamination and increasing possible health risks for swimmers. Remember: the solution to this is not more chlorine! CYA needs to be reduced before you add more chlorine to the pool.

Inaccurate Alkalinity Readings

High cyanuric acid levels can also lead to false total alkalinity readings. It can add to your carbonate alkalinity, which is part of total alkalinity. So, high CYA levels can give you incorrect total alkalinity readings.

Unsanitary Water

Since there’s less chlorine available to sanitize your pool water in a pool with high CYA, the pool will also be unsanitary. There may be high levels of bacteria, algae, and other unwanted contaminants built up in your pool that have not been sanitized yet.

Low pH

High levels of cyanuric acid can also lower the pH of your water. This can lead to further complications with chlorine effectiveness and make it more difficult to maintain a safe and comfortable swimming environment, not to mention the damage it would cause to your pool plaster or vinyl liner.

Step-By-Step Process: How To Lower Cyanuric Acid In Your Pool By Draining

Dealing with high CYA levels? The most common and effective way to lower the levels is to partially drain your pool water.

Step One: Test the Water

The first step in lowering cyanuric acid levels in a pool is to test the water to determine the current levels present. You can read my article on testing cyanuric acid in your swimming pool for all the steps.

Step Two: Identify the Cause

It’s essential to identify the cause behind the high levels since the issue can stem from various reasons. Identifying the source of trouble allows for efficient and targeted problem-solving and preventing future occurrences, so don’t skip the diagnostic step!

Step Three: Calculate the Amount of Water to Drain

Lowering cyanuric acid levels requires draining and replacing some of the pool water. As a basic rule of thumb, the percentage of the pool to drain equals the percentage to be reduced to restore regular CYA levels. For example, a pool with 80 ppm CYA requires a 50% drain-and-refill of water to get the level down to 40 ppm.

However, if you have CYA levels over 100, you may need to drain the water completely.

Step Four: Drain the Water

Partially drain your pool using a submersible pump or a store-bought hose siphon. Alternatively, you could also use your filter by setting your valve to “drain” or “waste.” Monitor the drainage carefully. If you are not draining completely, avoid getting the water below the skimmer to prevent damage to the equipment. If you need to drain more water past the skimmer, refill the pool first and drain again.

If you need to drain the pool entirely, I recommend hiring a professional, as there are many risks involved with draining the pool.

Step Five: Refill and Retest

Once you’ve drained out enough water, refill your swimming pool with fresh water and retest your pool chemistry. If you need to reduce some more, continue draining and refilling your water until you reduce cyanuric acid levels to the normal range between 30 – 50 ppm.

Step Six: Monitor and Maintain

Keep an eye on the cyanuric acid levels in your pool regularly. This will ensure that the levels remain within the recommended range and that the pool water is safe for swimming. Plus, by adding a cyanuric acid test strip to your weekly routine of testing water chemistry, you can avoid the hassle of draining and refilling.

How To Lower Cyanuric Acid Without Draining

Using a cyanuric acid reducer is an alternative option to avoid water waste and the expensive pumping, re-filling, and chemical balancing costs. A reducer neutralizes the acid, disintegrating the CYA at a molecular level. Here’s how to use it:

  1. Make sure your pool is at least 65°F, and do not add any algaecides, clarifiers, or phosphate treatments for one week prior.
  2. Test your water for chlorine and CYA. Make sure your chlorine levels are a little lower since chlorine can sometimes attack the active ingredient in a reducer, hampering its effectiveness.
  3. Test your water to ensure your pH and total alkalinity are also in the proper range.
  4. Add the remover evenly around the pool’s perimeter and circulate the water using your pump for 4-6 hours afterward.
  5. Retest the chlorine and CYA levels to ensure everything is in the proper range.
  6. After seven days, if the CYA levels are still high, a second dose may be necessary.

If you have further doubts, shoot me a message. I’ll be happy to step in and help out!

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