Cyanuric Acid for Pools: What You Need to Know in 2023


by Rick Patterson

As you know, it takes a lot of chemicals and a perfect balance to ensure your pool is crystal clear and safe for swimming. Sometimes you may feel like an alchemist mixing potions in a pool-size cauldron. (Okay, I do and it makes it more fun.)

You’ve mastered chlorine and measure it frequently to fight the cmonstant battle with algae and other baddies that may try to contaminate your beautiful backyard oasis. But wait! Your chlorine is disappearing faster than usual and you’re having to add more at an alarming rate. What’s going wrong?

Let me introduce you to the newest weapon in your pool care arsenal: cyanuric acid. This little miracle worker is going to be your best friend to protect your precious chlorine and keep your pool clean and sparkling all summer long.

What is Cyanuric Acid?

Cyanuric acid, as its name suggests, is an acid. (Feel smarter yet?) It’s actually a pretty weak acid, commonly sold as white crystalline powder when not pre-mixed with chlorine. It dissolves slowly in water and has hardly any effect on a pool’s pH.

You may have heard it called CYA, pool stabilizer, pool conditioner, or chlorine stabilizer. It’s all the same stuff. It’s an incredibly useful pool treatment that comes in several forms:

Dichlor = Pool Shock

Sodium Dichlor = Stabilized Chlorine (colorless, solid granules)

Trichlor = Chlorine Tablets or Sticks

Cyanuric acid is sold in liquid or granule form and is sometimes combined with chlorine. In this combined state it is called stabilized chlorine. You might see it called trichlor when it’s mixed with chlorine tablets or sticks and dichlor when it’s mixed with pool shock.

A Quick Chemistry Refresher

Cyanuric acid is a chemical compound in the triazine family, which basically means that its chemical makeup includes three nitrogens and three carbon atoms. It forms a weak and temporary bond with chlorine, which affects the chlorine more than the cyanuric acid itself. We’ll discuss that in a bit.

Chemically speaking, sodium dichlor is made up of one cyanuric acid molecule with two chlorine atoms and one sodium atom. This combination forms stable chlorine, which comes as a colorless solid.

How Cyanuric Acid Works

Cyanuric acid is used in swimming pools to lower the rate of photochemical reduction of chlorine, hypochlorous acid, and hypochlorite ion. That’s just a fancy way of saying it protects your pool’s chlorine from the effects of sunlight.

Once you add chlorine to your pool, the big yellow thing in the sky goes to work burning off the chlorine through chemical reactions, seriously decreasing the power of the chlorine in your pool water. In fact, the sun can eat up to 1 ppm (part per million) of chlorine every hour if it’s not protected.

The cyanuric acid extends the life of the chlorine by shielding it from ultraviolet rays. Without it, the ultraviolet rays from the sun would break apart the chlorite ions, allowing the chlorine to just evaporate into thin air. It literally stabilizes the ion, making it resistant to any chemical changes.

When you add cyanuric acid to your pool, it binds to the free chlorine floating around to form a compound that’s stable in sunlight. The reaction can also go the other way and release free chlorine.

As free chlorine gets used up, the cyanuric acid provides a backup of cleaning potential that’s safe from the sun. The free chlorine in your pool will then be available for sanitizing far longer than it would be without using stabilizer.

But just like wishing for immortality from a magical genie, there’s a catch. The increased lifespan of chlorine means it’s weaker than it was before.

Longer life = Decreased cleaning power

In other words, it takes stabilized chlorine longer to kill bacteria than it takes chlorine without stabilizer. As you can see, cyanuric acid is very useful but can be a double-edged sword, both increasing chlorine’s lifespan and decreasing its disinfecting power in your pool.

Why You Need Cyanuric Acid In Your Pool

Studies show that direct sunlight can decrease chlorine levels by up to 90 percent in two hours. And not just that, but the summer heat that warms your water can also be a breeding ground for bacteria, which also uses up chlorine more quickly.

What? That’s crazy, right? I know you’re starting to see dollar signs dance in your eyes, thinking of all of the chlorine you’re going to have to buy to keep up with the sun’s depleting effects. Not to worry, though, this is where cyanuric acid comes in to save the day.

Imagine cyanuric acid as a protective forcefield around the chlorine in your pool. It shields these cleaning molecules from ultraviolet destruction, extending the lifespan of the chlorine you just added. It’s a miracle worker in many ways, allowing you to manage your pool’s chemistry with minimal effort.

Cyanuric acid is a very important part of a good pool care regimen. It keeps your chlorine levels in check all summer long, without you having to constantly add more and more chlorine to your pool. 

Is It Safe?

Absolutely. Although cyanuric acid is an acid, it has a low level of toxicity. Adding it your pool will not cause any serious health concerns for swimmers. However, it’s the amount  of cyanuric acid in your pool that could cause problems. 

If you have high-levels of this chemical in a pool, your friends, family, and pool party guests may be at risk because of the chlorine’s diminished ability to kill bacteria and viruses. This is not due to cyanuric acid itself, but rather how it interacts with chlorine.

These same concerns would be present if you were lax about measuring and adding chlorine to your pool, in general. 

Optimal Levels of Cyanuric Acid

According to the Pool & Hot Tub Alliance, the ideal range for cyanuric acid should be between 30 and 50 ppm (parts per million) when used. The concentration should not exceed 100 ppm, which is the absolute upper limit prescribed by the World Health Organization

Keeping your levels around 50 ppm will ensure that your chlorine is still able to do its job without getting demolished by sunlight. Remember, more cyanuric acid doesn’t mean more protection, it will actually just decrease your chlorine’s efficacy.

Note: Cyanuric acid is not recommended for indoor pools that do not receive direct sunlight.

Why These Levels Matter

Pools that contain little or no cyanuric acid are going to eat through chlorine like crazy, especially if your pool is in direct sunlight for any portion of the day. You could order truckloads of chlorine and still might not have enough to keep your pool sanitized.

So unless you have little elves producing chlorine for you in your basement, you’re going to want to protect the chlorine that you add to your pool. Adding cyanuric acid in the right amounts is going to save you a lot of money in the long run.

However, since cyanuric acid decreases the cleaning power of your sanitizer, you want to make sure you get the levels just right. If you add too much, the chlorine loses all effectiveness and you’ve just wasted money on two chemicals.

Even if you add the right amount of cyanuric acid, you need to test for it regularly. Because unlike chlorine, it doesn’t degrade and continues building up. It stays in your water for a long time. With too little cyanuric acid, your chlorine disappears quickly. With too much cyanuric acid, your chlorine loses it’s cleaning power.

With me so far? Okay, good. So now you’re probably wondering how to test for this. 

How to Test for Cyanuric Acid in Your Pool

Now that we know that cyanuric acid stays in your pool water for a long time and doesn’t get used up the way chlorine does, testing often is super important.

Most complete pool test kits come with a test for cyanuric acid but you can also get separate tests or test strips to check your levels. If you don’t want to do it yourself, you can always take a sample of your water into a local pool store that offers free water testing.

If the cyanuric acid level is anywhere between 30 and 50 ppm then you’re in good shape. You can crack open a beer and relax by the pool. 

You probably won’t have to add cyanuric acid to your pool after your first dose of the season unless you’ve had a giant pool party with lots of kids or a massive rainfall, either of which may have thrown off your pool’s chemical balance.

What To Do If Your Levels Are Too Low (Or Too High)

So you’ve tested the cyanuric acid levels in your pool and they’re below 30 ppm… what now? 

Well, that’s the easy one. You just need to add a bit more and you’re good to go. Need a refresher on how to add cyanuric acid? We got you covered: jump down to the next section.

If your levels are too high, on the other hand, it’s a bit more tricky to solve. See, over time, cyanuric acid can build up in pool water, since it doesn’t disappear on its own. If you’re seeing a reading much higher than 50 ppm you really need to lower your levels so that you’re not reducing the effectiveness of the chlorine. 

The easiest and most affordable way to reduce cyanuric acid is to drain some of the water from your pool and add some clean water. This dilutes the cyanuric acid and brings the water back in balance, upping the chlorine’s purification power. Don’t forget, however, that draining and refilling your pool means you’ll have to test and balance your chemicals again. 

Now, if you’re living in an area that’s going through a drought or has placed water restrictions on residents, perhaps draining your pool (or even a portion of your pool) is not an option. In that case, there are cyanuric acid reducer products on the market that will bring down the levels in your pool but only if they are 100 ppm or higher.

How to Add Cyanuric Acid to Your Pool

If your levels are too low and you need to bring your levels up above 30 ppm, it’s time to add some cyanuric acid to your pool. 

This process usually involves dissolving some granules in a bucket and pouring it around the edges of your pool. However, there are some companies that recommend adding it directly to your pool.

I’m sure they have their reasons for this but since cyanuric acid dissolves super slowly, it really does make more sense to use the bucket method. Just make sure to follow the manufacturer’s instructions regarding amounts.

If you currently use chlorine that comes in tablets, sticks, or granules, it will actually already contain cyanuric acid as an active ingredient, so you’ll probably only need to add it at the beginning of the pool season.

Each time that you add chlorine after that, you’ll be testing chlorine levels and keeping your cyanuric acid levels in-check. 


If you have an outdoor pool, there’s no getting around it: you’re going to need cyanuric acid to protect your pool from chlorine loss.

Without it, any chlorine you add will be gone in a matter of hours, completely wasting your time and money (not to mention leaving your pool open to bacteria and algae attacks).

It’s one more chemical you’ll need to add to your pool and keep balanced, but with proper care and testing, will protect your chlorine, your wallet, and your sanity in the long run.

Categories: Pool Care, Pool Chemistry