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Cyanuric Acid: Good or Bad?

Cyanuric Acid: Good or Bad?

Cyanuric acid (CYA) is a chlorine stabilizer that is widely used in residential and commercial pools and spas. So why are so many people, including health officials, split on whether it is beneficial or harmful?

The Good: When added to pool/spa water, CYA reduces the amount of chlorine loss from the sun’s ultraviolet rays, thereby reducing the amount of chlorine needed to maintain the proper level of sanitizer in the water. Less chlorine needed = more money in your pocket.

The benefit of using CYA is that it allows the free chlorine residual to last 3‒5 times longer in the water, which means more chlorine is available to do what it is intended to do — protect bathers’ health, the #1 goal. Given that fact, why is it that some states ban the use of CYA?

The Bad: We often say, “If some is good, then more must be better!” This is true in a great many things, but not in chemistry. Adding too much CYA can lead to overstabilization, which then diminishes chlorine’s effectiveness as an oxidizer and a sanitizer. Did you know that products like trichlor and dichlor, which are referred to as stabilized chlorine, already contain CYA? Be careful how much CYA you add if you use one of these products, or you could be headed right down the road to overstabilization. On the other hand, unstabilized chlorine products — such as sodium hypochlorite, calcium hypochlorite, and lithium hypochlorite — do not have any CYA in their formulation.

This may be a controversial statement to some people, but there are studies that show CYA levels over 50 ppm offer no additional benefits. In other words, it’s a waste of money to maintain higher CYA levels. And then there’s the issue of toxicity. Although there are no known cases of CYA poisoning, most health officials usually limit CYA levels to 100 ppm, some states recommend a lower level for spas, and some jurisdictions ban the use of CYA altogether. Most people, however, agree that keeping CYA levels in the range of 30 to 50 ppm is optimal.

Another factor to consider is the effect that CYA has on a total alkalinity reading. Total alkalinity is the sum of all titratable alkaline substances (carbonates, bicarbonates, hydroxides, cyanurates, and
other components). Therefore, the total alkalinity titration measures both carbonate and cyanurate alkalinities. This affects water balance calculations because the alkalinity term in the Saturation Index equation is strictly carbonate alkalinity. So high CYA levels can lead you to think you have the proper or high carbonate alkalinity levels. To determine the true carbonate alkalinity value, subtract one-third of the CYA reading from the total alkalinity reading.

The Takeaway: Cyanuric acid can most certainly be beneficial. Just remember to test CYA levels monthly, adjust your total alkalinity reading when using CYA, and do not feed “stabilized chlorine” products when your CYA levels exceed 30 ppm.