CYA (cyanuric acid): what it is and how it affects pool water

Cyanuric acid (CYA) is one of the key water parameters in outdoor pools, directly affecting chlorine effectiveness and overall water balance.

What is CYA?

CYA (cyanuric acid) is a stabilizer that protects chlorine from degradation due to direct sunlight.

Why is the standard lower for public pools?

The recommendation to limit to 15 ppm is related to safety.

In public pools, fecal contamination (AFR) may occur. To destroy pathogens such as Cryptosporidium and Giardia, a certain contact time between chlorine and water (CT) is required.

At CYA levels above 15 ppm, effective disinfection becomes practically impossible.

How to lower CYA levels

The simplest and safest way is to dilute the water. You need to partially drain the water and add clean water.

The math is simple:
to reduce the CYA level by half — you need to replace half of the water volume.

It is important to note that cyanuric acid can settle on pool surfaces.

How to prevent CYA buildup

The best strategy is to not let it build up.

To do this:
— use unstabilized chlorine
(sodium hypochlorite or calcium hypochlorite)
— monitor CYA levels regularly

Conclusion

Cyanuric acid is not just an "additional parameter" but a critically important element of water balance in an outdoor pool.

It simultaneously protects chlorine but can reduce its effectiveness when in excess.

Therefore, the main rule:
control and balance, not maximum values

More useful information is available on our website.

Frequently Asked Questions

Why does chlorine stop working effectively at high CYA levels?

Because most of the chlorine binds with cyanuric acid and becomes less active. Active HOCl sharply decreases, and even at normal chlorine levels, disinfection effectively weakens.

Can I just add more chlorine if CYA is too high?

Technically, yes, but it's inefficient and expensive. For example, at 100 ppm CYA, you would need to maintain approximately 7.5 mg/L of free chlorine instead of standard levels. This increases costs and the load on the system. The correct solution is to reduce the CYA level.

How to quickly lower cyanuric acid levels in a pool?

The only effective and safe method is partial water replacement. If you need to halve the CYA, approximately 50% of the water should be replaced. Other "methods" usually do not work or are not economically viable.

Share:
Link copied!