The Ultimate Guide to Using Cyanuric Acid

This guide will show you everything you need to know about using cyanuric acid in your pool.


  • What cyanuric acid is
  • What it does for your pool & why you need it
  • How much you should use
  • How to add it to your pool
  • Plus lots more

So if you want to become an expert on using cyanuric acid in your own pool, this guide is for you.

Let’s dive in.

What is Cyanuric Acid?

Cyanuric acid is a chemical compound that forms a weak bond with the free chlorine in the pool water, protecting it from the sun’s ultraviolet rays to reduce chlorine loss. [source].

This chemical compound is called triazine and is composed of 3 carbon and 3 nitrogen atoms.

Another derivative of the compound is melamine, which is used as a fire-retardant as well as a pesticide. But rest assured, the compound known as cyanuric acid is formulated slightly differently than melamine and is completely safe.

Cyanuric acid (CYA) is sold both in liquid and granular form, and some products even have it mixed right in.

Trichlor and dichlor both contain CYA to stabilize the chlorine, which kind of helps take the guesswork out of how much to use.

What Does Cyanuric Acid Do?

Chlorine performs its own slightly complicated process in your pool. And even if it measures within range, only part of it is free to sanitize.

This part is called free chlorine and it’s the most important factor in keeping your pool safe.

But there is also combined and total chlorine.

Combined vs Total Chlorine

Combined chlorine is what has already been used killing all the bad stuff in the water. And total chlorine is the sum of both free and combined.

Confused yet?

The important thing to understand here is that the free chlorine is what you’re trying to keep alive, and is one of its biggest enemies is sunlight.

UV rays break the chlorine molecules apart and causes it to evaporate. In fact, during a bright, sunny day, your pool can lose 90% of its free chlorine within just two hours.

But that’s not all.

The heat from the sun also plays an important part in this process. Because heat causes bacteria to grow faster, your pool uses more of its chlorine to kill it.

So, sunny days with high temps can zap your pool’s sanitizer levels almost as fast as you can pour the stuff in.

That’s where CYA comes in.

This chemical binds to the weak ions that the chlorine breaks down into and acts like a sunscreen to protect them, which allows the chlorine to work up to five times longer than it would without it.

It also can’t be destroyed by other chemicals so it’s sort of its own defense system.

Why Do You Need Cyanuric Acid?

What all this means is that in order to keep your pool clean, you would need to add almost ten times as much chlorine as normal during the sunny times of the year.

And isn’t that, in fact, when we swim the most?

This not only gets expensive, but it’s also a huge time-waster.

You could be testing your pool levels every couple of hours and adding more chlorine, or you could simply add some CYA and go back to testing normally.

Drawbacks of Using Cyanuric Acid

Just like with all the other chemicals you add to your pool, there is such a thing as too much CYA.

In fact, adding too much will completely destroy the effectiveness of your chlorine. So now, instead of wasting time and money on one chemical, you’ve done it with two.

Also, when CYA is too high, there’s not much you can do to decrease it except to dilute it.

And to do this, you’ll need to drain some of the water from the pool and add more, which is time-consuming and wasteful. Not the ideal way to spend your Sunday.

The moral of the story: a little CYA goes a long way. Add a little at a time and test your levels in between.

How Much Cyanuric Acid Should You Use?

The amount of cyanuric acid you should use is a little tricky, since like we said earlier, too much of a good thing is not always a good thing.

What the government recommends is that you keep CYA levels no higher than 100 ppm (parts per million).

But this isn’t necessarily based on making sure it’s doing its job properly, rather it’s more of a safety level for swimmers to keep them from having negative reactions to the chemical.

For the purposes of keeping your pool clean, inching much more above 50 ppm of CYA can start to affect the effectiveness of chlorine, so that’s about where we keep it—usually between 30 and 50 ppm.

And if you can’t seem to get a good reading from your test kit, take it to your local pool store to have it analyzed. This, by the way, is a good thing to do once a year anyway. And not just for CYA, of course, but for all your chemicals.

Using Chlorine Tablets

Adding CYA to your pool is fairly easy.

If you’re using chlorine tablets, they already have some in them, so you won’t need to do anything else. However, these don’t allow you as much control over your levels as using the chemical separately does.

If you always use tablets, it’s possible to start noticing higher levels of CYA when you test. This is because you’re constantly adding it, even if your pool doesn’t need it. To avoid this, you can do one of two things.

First, you can use your tablets except when your CYA levels are already optimum. In other words, if your CYA levels are between 30-50 ppm, you’ll only add straight chlorine instead of the tablets. This will help you avoid adding too much of the acid.

Second, you can maintain the most control by always using chlorine and CYA separately. This way, you can measure and decide exactly how much to add of each one.

And because CYA isn’t easily killed off, you can probably get by with adding it to your pool every six months or so.

How to Add Cyanuric Acid to Your Pool (Safely)

Even though it’s somewhat milder than other acids, CYA is still an acid and should be treated as such. That being said, you’ll need to protect your eyes and skin properly.

So be sure to put on a good pair of safety goggles and chemical-resistant gloves before you even open the container.

Each manufacturer has its own instructions about how to add the chemical, so read those before you start. Some say to pour it directly into your skimmer without diluting it first. But most of the time, you’ll need to mix it with warm water in a five-gallon bucket.

To do this, fill the bucket about half full with warm water (not hot, but warmer than room temperature).

Then, add your recommended dose of CYA to the bucket. Again, be sure to read the directions on your product, but usually a dose is 13 ounces. This will give you about 10 ppm for 10,000 gallons of water.

To figure out how much you need, you’ll need to know the size of your pool (in gallons) and the current CYA level.

For example, if you have a 20,000 gallon pool and the current CYA level is 20 ppm, you’d need to add about 3 doses of the product to bring it up to 50 ppm. But it’s best to do this one dose at a time unless you’re starting out from zero. Then, you can probably safely add two doses before testing.

Next, you’ll pour the bucket mixture right into your skimmer and run the pump for 4-6 hours.

Note: CYA can damage vinyl liners or filters if added directly to them. And some manufacturers actually recommend this. But even if they do, it’s best to add it to the skimmer instead.

How to Lower Cyanuric Acid Levels

Just like knowing how to raise the CYA level in your pool, it’s also crucial that you know how to lower it.

But first of all, if you do have too much CYA, you need to know why. If you’re not sure, check the package of the sanitizer you’re using.

Your product may not include cyanuric acid in the title, even if it contains it. Instead, it’s probably labeled “stabilized chlorine.” Or it will contain the chemicals trichloroisocyanurate, potassium dichloroisocyanurate, or sodium dichloroisocyanurate.

All of these contain CYA and if you are using them, you are adding the chemical to your pool every time you add it.

If you’ve unintentionally been using stabilized chlorine and noticed your CYA levels creeping up, switch to straight chlorine until you need to add more CYA. But for now, you need to get those levels lowered if they’re above 50 and there’s really only one effective way to do this—diluting the water.

In order to dilute your pool and lower your CYA level, you’ll need to drain a little of the water and add fresh water to make up the difference.

How much you drain will depend on how high your CYA level is. If it’s just a little high, you can probably get away with just draining a few gallons. It’s not an exact science, but if your CYA level is up 10%, you can start by removing about 10% of the water.

This is not exact because CYA can hang around any calcium scale or plaster in your pool, or it can just be more concentrated that you realize. So, draining old water and adding fresh water is usually more of a trial and error thing.

But if your CYA level is up by a lot, you may even have to drain the entire pool and start over.

Draining a pool completely is no easy feat and best to be avoided at all costs, though. So, there are a couple of other options you can use to lower your CYA levels.

One is to wait for a big rain. If you live in an area that gets frequent rainfall, you’re in luck. One or two big rains will probably bring that level down pretty quickly.

The second thing you can do is purchase a cyanuric acid reducer. These products are not readily available, though, and from what we hear, not extremely effective.

However, in some areas, it’s almost impossible to drain a pool without going through a lot of red tape with the city. So, it’s understandable why people might need to try this option first.

Test Your Pool Regularly

Whether you use CYA or not, testing your pool is the most important thing you can do for the health of your water.

We recommend doing this at least once a week, but under certain conditions, you may need to do it more.

For example, if you have a larger amount of swimmers than usual, your pH levels can become quickly unbalanced. Or if you get a lot of rain, it can dilute your pool and alter the chemicals.

Cyanuric acid levels don’t change much unless your pool does get diluted with a lot of rain. So keep in mind that you’ll probably only have to add it once or twice a year. But your other chemicals can change a lot over the course of a week.

And if you keep your CYA at around 50 ppm, you’ll need to make sure you keep your free chlorine at around 3 ppm to help them work together optimally.

Bottom Line

Cyanuric acid is an effective chemical many pool owners use in order to keep their chlorine functioning as it should. But it’s important to know how and when to use it.

The best thing you can do for the safety of your swimmers is to test your water at least once a week and add CYA only when needed.

Scroll to Top
Scroll to Top