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What is Cyanuric Acid? How does it affect pools if it’s too high?

high cya


First, let’s remind ourselves what CYA does and why high levels in the pool is such a big deal. CYA, also known as chlorine stabilizer, is like sunscreen for the pool. Before its discovery in 1956, chlorine used to be added to the water daily. Plus the regular practice of adding extra amounts of liquid sodium hypochlorite in the late afternoon or evening to help combat chlorine-loss during the day.

Unlike some other sanitizers like ozone or AOP, chlorine is highly susceptible to sunlight which breaks the sanitizer down, giving it a half-life of only 30-45 minutes. It doesn’t take a lot of “figuring” to learn how quickly that can become a problem. When a stabilizer like CYA is absent, you have to continuously add chlorine to the pool to make up for the amount constantly being “burnt off” by the sun.

bright sun on pool

The sun is fun but it will destroy your chlorine levels!

Without getting too technical, CYA is used to protect free chlorine from UV degradation (sunlight). On a molecular level, CYA works by attaching to free chlorine in the water through a weak nitrogen-chlorine bond. While attached, chlorine is protected from the sun. However, the unstable nitrogen bond allows chlorine to “let go” when called upon to do its intended job of killing bacteria and harmful pathogens. 

Do you recall the conversation we had not long ago about cyanuric acid (CYA) and salt chlorine swimming pools? Many pool professionals got pretty excited about the topic and the response was very insightful to say the least. You can check out the original post here.


Here’s where we find ourselves stuck between a rock and a hard place. The pool needs CYA, but that creates a new set of problems. As CYA levels get too high it can “lock up” chlorine making it less reactive. 

The official recommendation is to keep CYA at levels of 30-50 parts per million. Some studies show we get 95% of the CYA value at just 20-30ppm. Basically, in this case less may be more!

As a convenience, cyanuric acid is added to many chlorine products. When CYA is an ingredient added to most chlorine tabs or shock, it can build over time. Trichlor and Dichlor are both commonly used forms of chlorine tablets, and both contain chlorine and CYA. That “two-in-one” convenience factor can raise CYA in the pool over time. 

Even with plenty of chlorine, high CYA may leave a pool looking dirty and gross.

Keeping a low CYA level starts to get difficult. Every time chlorine is added to the pool, the chlorine stabilizer level goes up. CYA negatively affects disinfection rates by binding to “free chlorine”—the killing form of chlorine—in pool water. CYA reduces kill rates and impacts oxidation reduction potential (ORP). 

Whoa there, what is ORP? ORP (oxidation reduction potential) is an electronic measurement of sanitizer effectiveness in water. It is a metric of the ability of a chemical substance to oxidize or reduce another chemical substance. The higher the potential for oxidation, the more efficient your sanitizer is at keeping the water safe for swimmers. 

It’s not technically a measurement of the sanitizer in the water. It’s a measurement of potential. You could have 0 chlorine with a high ORP and guess what, no killing power! But ORP is a tool to see how healthy the residual sanitizer in the water is. While ORP does not measure the amount of chlorine, it does give us a “real-time” indication of how chlorine is performing in the pool and how much “killing power” the chlorine actually has.

As more chlorine products are added, CYA can increase, which can decrease chlorine effectiveness. The end result is an endless cycle of adding more chemicals and shock to the pool to make it more effective, which then increases CYA and well…you get the idea. All of your focus turns to keeping the level of CYA from getting out of control. 


In the advanced oxidation process (AOP), UV-C reacts with ozone to create hydroxyl radicals—the most powerful oxidizer for residential pools. It kills what makes swimmers sick, helps you reduce overall chemical use, makes the water crystal clear, and destroys chloramines.  

CYA does not directly affect an ozone or AOP system. It isn’t required to protect AOP from sunlight either. UV from the sun does not destroy ozone, and it does not create AOP. 

If CYA does not affect AOP or ozone, does CYA matter at all? Here’s the rub. Many ozone and AOP users prefer to keep chlorine levels on the lower side, but high CYA prevents this by making chlorine less effective. You may want a chlorine level close to 1ppm.

But when you do the math, high CYA levels may require chlorine levels of 5 ppm or more to remain effective. For this reason, low CYA can be very important if you want the full benefits of ozone or AOP. 

chlorine tablet by pool

AOP and low CYA can help keep those chlorine levels low, saving you money!


Salt chlorine generators produce a chlorine residual sanitizer in the water in the form of “free chlorine” (the killing kind). With salt systems, free chlorine is produced on-site through the chemical process called electrolysis. Since salt equals chlorine, some CYA is still needed to do what it does best—protect the chlorine. 

The chlorine generated from salt systems creates a consistent “baseline” in the pool, which also helps you avoid the need to shock. So CYA is needed for a salt system, but it is only added manually. 

While CYA is required for a salt pool, here is a cool feature of the chlorine generator. Since the cyanuric acid is only added manually when you need it, you have total control.It won’t build up over time if you are not also using tablets or shock. 

relaxing in a salt pool

A salt chlorine generator can really take the stress out of pool care

Chlorine generators electrically create Hypochlorous Acid (HClO) in the pool water. They do this with zero additives—no CYA, no clarifiers, no binders. This is the purest form of pool chlorine. And, it’s being generated right in the backyard with zero chemical storage. 

What does this mean to you? Since you’re hand-feeding CYA to the pool instead of it being added via tablets/shock, this puts you in control so that you can focus on maintaining the perfect water balance.


We know pool care can be complicated with a ton of information to sift through. Hopefully the info above makes the fight against CYA a little easier for you. 

If your pools are only running chlorine for sanitizing, now is the time to nip your CYA problems in the bud! You can defeat pool chemistry problems by combining the best sanitizer technology including AOP, ozone/UV and salt chlorination. 

The Complete Modern Pool is a total package. Ozone or AOP help with keeping chlorine levels lower and making the pool safer. A salt generator creates pure chlorine and you don’t have to worry about high CYA problems. It’s a real modern solution!

The modern pool uses fewer chemicals and is better for the environment. It’s the whole package! Click here to learn more about innovative equipment from CMP that makes pool care easy, or reach out to your sales rep for more information.


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