Pool Plant Courses - Blog

Cyanuric acid is mostly used in outdoor pools. The reason for this is that chlorine is broken down by ultra violet light. Sunlight contains ultra violet light and when the sun shines onto an outdoor pool the chlorine gets depleted very quickly. The pool plant operator needs a way of 'stabilising' the chlorine and that's where cyanuric acid comes in. Cyanuric acid binds with the hypochlorous acid (the disinfectant in chlorine) and makes it more resistant to degradation by UV. The drawback is that it also makes the hypochlorous acid less effective as a disinfectant and for that reason, higher free chlorine residuals must be maintained when using cyanuric acid (2.5 - 5.0 mg/l).

Dosing the correct amount of cyanuric acid can be tricky. Too little and you won't stabilise the chlorine enough, too much and you will over-stabilise and the hypochlorous acid will not be available to act as a disinfectant. The pool plant operator must ensure that the cyanuric acid levels are kept below 200 mg/l, with the ideal range being 50 - 100mg/l. The most effective way of keeping cyanuric acid levels in check is through dilution with fresh water.