Cyanuric Acid (Pool Stabilizer) – A Pool’s Best Friend, or Worst Enemy?

cyanuric acid

Cyanuric acid chemical makeup

Cyanuric acid, also known as pool stabilizer or conditioner, is my best friend in the hot Florida summer months. The level has to be monitored just as much as chlorine, and if left unchecked it can end up causing one of the worst problems a pool owner can face.

Cyanuric acid can be found in many chemicals added to a swimming pool. It’s most notably found in dry granular and concentrated pucks of chlorine. Though it can also be added by itself as raw cyanuric acid/stabilizer. By adding in dry chlorine or tabs you are usually adding stabilizer along with them. This is a very good thing in the majority of cases, unless it’s the only form of chlorine you are adding and your cyanuric acid level is high.

What’s its role:

Cyanuric acid performs one crucial role: It helps stabilize and protect the existing free chlorine in the pool water from being burned up naturally by the sun’s intense ultraviolet rays. This makes the balance of sanitizing chlorine last longer, which in turn helps keep the cost of maintaining the pool at a manageable level.

Recommended level:

A safe level for the cyanuric acid in most pools is between 30-50ppm (for salt system pools this number is between 60-80ppm) and most pool testing strips can provide this level. Too little stabilizer, then the free chlorine in the water won’t last very long against the sun’s UV rays, which decreases the sanitizing power of the chemicals. You will find yourself having to keep adding chlorine or shock to keep your pool from turning green. The price of all that chemical can quickly put a drain on your wallet.

So what happens when the cyanic acid level is too high? The stabilizer binds to too much of the free chlorine and reduces its power against killing the bacteria and algae in the pool. The water will also become very cloudy, and if left unchecked green very fast. The most common mistake I see when this happens is a worried homeowner will go straight to the pool store and buy pool shock, which more often than not contains cyanuric acid and just compounds onto the problem. No matter how much chlorine you put in your pool at this point, the pool will continue to turn greener and slowly become toxic as the sanitizing power of the chlorine is drastically gimped. I call this situation “chlorine locked”.

Lowering the cyanuric acid level:

There’s only one sure fire way to lower the level of cyanuric acid in a pool that’s become chlorine locked because the stabilizer is too high. Drain it. Pure and simple, you have to remove the water that is high in cyanuric acid and replace it with fresh water. Say, for example, your pool is at 90ppm of cyanuric acid. You will have to drain half of your pool water and replace it with fresh water to dilute the stabilizer to a safe level of 45ppm. You can try and lower that acid level other ways if you want, by using oxidizers, various concoctions, or black magic, but as a pool professional I’ve tried many options to spare the homeowner from having to drain and refill their pool, and the only viable option I’ve found is to just drain and replace the water.

Keep in mind that that drained water has to go somewhere and it can’t be the yard around the pool. When you drain your pool, the wetter the surrounding earth around your pool is, the more likely you can have a problem with the pool cracking or in severe cases literally popping out of the ground. Not to mention refilling all that water will cause a large dent in your wallet, though some utility companies will give you a break on the sewage charge of the water if you notify them in advance that you are refilling a pool.


Test your water occasionally and watch the cyanuric acid level. If your test kit doesn’t test that level, get a new one. It’s an expensive mistake some people only learn from the hard way. If you notice the level getting higher than the acceptable range for your pool, stop adding in chlorine tabs or dry chlorine and only add in wet until that level balances back out.

Not sure if your pool has too much stabilizer being used? Contact us and we can easily let you know.


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9 thoughts on “Cyanuric Acid (Pool Stabilizer) – A Pool’s Best Friend, or Worst Enemy?

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