Cyanuric Acid (CYA)

Often, at your local pool shop, cyanuric acid (CYA) is in powder form and is often labeled as sunscreen or sunblock. CYA works by binding to the free chlorine in your pool which protects it from being killed off by the sun’s UV light. Remember, CYA will extend the life of your pool chlorine. So, if you use liquid chlorine with CYA, then the amount of chlorine you need to keep the water safe is reduced. And this saves you a lot of money.

Remember that high CYA levels in your pool are dangerous. It is important that your CYA levels are checked regularly so that the free chlorine remains effective and can keep the water safe for swimmers.

Chlorine Tablets are full of CYA

Using chlorine tablets continually, will increase the CYA levels in your pool. This is because they contain 55% of CYA. So each tablet you add to the pool will increase the CYA level. Remember, if you use these tablets constantly then your CYA level will get too high. And, once the CYA level get too high, it can cause staining, cloudy water and make the pool water unsafe.

chlorine tablets
Chlorine tablet contain 52% CYA. Continued use will cause the CYA levels to increase.

Cyanuric acid reducer

These days there are a lot of products that claim to reduce the CYA levels in your water. Most of these products are made by respected brands in the industry. So if you have high CYA and don’t want to drain any of your water then these products may be worth a try. On the other hand, draining part of your pool water and refilling will also achieve the same result.

Testing the CYA levels in your pool

You can test your CYA levels in two ways. First, you can use a pool water testing strip as shown in the video. Second, you can take a water sample to your local pool shop for testing. Generally, they will help you with this test and also offer free advice. You can increase the CYA levels in your pool by adding CYA. Remember, if your pool runs only on liquid chlorine then proper CYA levels are vital. This is because if your CYA levels are low then your chlorine use will increase substantially.

High CYA can lead to purple staining

As the image below shows, high CYA levels, when combined with copper, can lead to purple staining on the pool walls and floor. The picture shows how this can look in a fibreglass pool. This type of staining is very uncommon. If your CYA levels are corre3ct then it is very unlikely that you will ever see staining like this.

It is caused when copper sulphate from algaecides combines with very high CYA levels in the pool. As they interact with each other, they leave a stubborn purple stain on the walls of the pool. If you have this type of staining and would like it removed there is more information about that online.

staining from CYA
This pool had excessive CYA levels so when copper based algaecide was added the walls turned purple.