A controversial topic in the world of swimming pools, but one that is worth understanding better. CYA, or Cyanuric Acid as it is known as, is a pool stabilizer and makes up just one part of the chemicals many people use to cleanse their pool and make it safe to swim in.

Although many people don’t see it as an essential chemical, it is the sort of product that will enhance the capabilities of the other chemicals, particularly chlorine. By adding CYA, the chlorine in your pool maintains its sanitising abilities for longer. Essentially, it keeps your water clean for longer by stabilizing the chlorine.

That might be the basic overview, but it goes on…

CYA Comes In Different Forms

Although you may have heard people talking about this chemical, you may be using it to treat your water already. This is because it is often added to chlorine and sold as stabilized chlorine. If this is the type of chemical you are adding to your pool, there is no need to add additional CYA. For some people, this is more convenient as they don’t have to get the measurment right before adding it to their water, but others prefer to measure it seperately so they can be accurate in their amounts.

CYA and UV Rays

UV rays can render the chlorine in your pool useless, evaporating almost three-quarters of the chlorine within hours of it being added to the water. This is where CYA comes in. It protects the chlorine from UV rays so it stays in your pool, and keeps it clean. When it does its job, chlorine kills bacteria which is the whole purpose of using it. the problem is, when it does this it becomes combined chlorine, no longer able to sanitise the water in the same way it did in its former state, total chlorine.

Cyanuric acid allows the chlorine to kill bacteria and contionue to do so, prolonging its effectiveness.

Why Should I Use CYA?

Unless you want to be adding chlorine to your pool water every other hour, CYA is an important chemical to include in your cleansing treatment. Cyanuric acid prevents the breakdown of chlorine when in contact with UV rays and makes it last up to 5 times longer than it would otherwise.

This ensures your pool is not at the mercy of bacteria and other contaminants and gives you the confidence to know the water is going to be safe for days.

Why Does Cyanuric Acid Get A Negative Rep?

A lot of the time, people are unsure about CYA often because accuracy is important. When you have high CYA it reduces the effectiveness of the chlorine, defying the point of using it in the first place. It also means there are two sets of chemicals in your pool that are not doing their job.

Sometimes, CYA levels are too high because the person adding the chemicals is already using stabilized chlorine. Additional CYA will reduce effectiveness. The alternative is to switch to a regular chlorine and add your own CYA but if you are experiencing high levels of it already, wait for the current batch to evaporate and add fresh water before doing so.

If the levels are particularly high some pools will require draining and refilling.

What Is The Optimal Level Of CYA In A Swimming Pool?

Depending on where you get your information from, a lot of people have different opinions on this. The World Health Organisation advises that you should maintain CYA levels in a pool at a maximum of 100 parts per million (ppm).

Others say 50 ppm is a better ratio as too much CYA prevents chlorine from being as effective. The general consensus for having too little is anything around 30 ppm and below.

How Do I Know My CYA Levels Are Off?

There are a few telling signs that your cyanuric acid levels are not right, most notably the formation of algae or cloudy water when the pool chemicals would usually be doing their job.

This can be down to several reasons such as a faulty filter but it is always best to test the water to see what exactly is causing the contamination.

How To Test CYA Levels

The most accurate way is to take a sample to a pool cleaning supply store. From there, they will have the equipment to take a proper reading to give you an accurate assessment.

Otherwise, a lot of people use test strips to continually monitor CYA levels. If your cyanuric acid levels are too high, you might find it hard to read the test strip. Also, turbidity test kits are popular and easy to use.

Check Your State’s CYA Laws

Because each state has its own regulations when it comes to swimming pools, chemicals, and CYA levels are something you have to comply with. These will vary from place to place so make sure you are keeping your CYA levels in line with local law.

Some will seem low when compared to others as they can vary from maximums of 30 to 100 ppm which sounds surprising.

How Often Should I Test My Pool Water?

Testing the cleanliness of your pool water is something you need to do regularly. The longer you leave it the worse the water can get but out of the summer months, once a week should suffice.

In the summer when the pool is used frequently, and the UV rays are greater, it is a good idea to test it twice a week. Stick to the same days every week and use a maintenance schedule. Your CYA levels shouldn’t fluctuate too much so keep an eye out for irregular readings and use a test kit to keep an eye on the chemical and pH levels.


It doesn’t matter what type of pool you have or use (a public pool will maintain their CYA levels), optimal levels of CYA help to keep the users safe by ensuring there is adequate sanitation.

Be sure to regularly keep an eye on the levels of all chemicals so you and your family can enjoy clean water every time you swim.