Letter to the Editor re: Cyanuric acid levels in pools

Monday, 11 April, 2016

Letter to the Editor re: Cyanuric acid levels in pools

Responding to the cyanuric acid article very well presented by Nick Rancis in the March/April Pool+Spa where several high levels of cyanurate are mentioned along with the kill times of various levels of chlorine and with a graph clearly showing these effects.

Trials and laborious testing done by myself and others in Australia, plus industry leaders in other countries, have concluded that the concentration of cyanurate in pool water — that’s outdoor pools only — which gives the greatest efficiency, plus provides for safe and comfortable swimming, is in fact between 15 and 20 mg/L (ppm). At this level, we can achieve approximately 93% efficiency of the stabiliser cyanurate. Doubling the cyanurate level to about 35 mg/L will achieve about 96% efficiency or chlorine protection by the cyanurate, so now we have twice the amount of this chemical in the pool for a 3% advantage. It clearly isn’t a sensible approach for many reasons and should never be taken to this level. This is why 15–20 mg/L of cyanurate should be used and adhered to.

Also, the graph shows chlorine levels of 0.25, 0.5 and 1.0 mg/L (ppm) when comparing bacteriological kill rates with cyanurate at 100 mg/L. Running the chlorine and cyanurate together at these levels will quickly cause uncontrolled algae and bacteriological growth and unsafe, if not dangerous, swimming conditions. In Australia, most states agree that it’s necessary to have a minimum chlorine concentration of 3 mg/L (that’s free chlorine) with an associated pH of between 7.35 and 7.45, for maximum chlorine sanitation along with swimmer comfort.

It’s a clear fact that the swim centres that have cyanurate between 15 and 20 mg/L in their outdoor pools, the free chlorine at a minimum of 3 mg/L and the pH between 7.35 and 7.45 have excellent water quality, safe and comfortable swimming conditions and usually no algae. These chlorine and pH levels are suitable also for indoor pools without supplementary oxidation processes, as long as the cyanurate isn’t used.

John McKenny


Image credit: ©FreeImages.com/Marcel Hol

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