Why is it tested?
Because the stabiliser accumulates in the water, does not decline on its own, and can only be seen by measuring it.
What does the stabiliser do?
According to WHO’s swimming pool guidelines, chlorinated isocyanurates are stabilised chlorine compounds, widely used in the disinfection of outdoor or lightly loaded swimming pools.
They dissociate in water to release free chlorine in equilibrium with cyanuric acid. A residual of cyanuric acid and a number of chlorine/cyanuric acid products remain in the water.
The practical benefit is clear: in an outdoor pool, sunlight destroys free chlorine quickly; the stabiliser slows that loss and keeps chlorine present through the day.
Why is there an upper limit?
Because cyanuric acid stays in the water and accumulates with every dose. Unless the pool water is diluted or partly refreshed, the concentration only rises.
WHO’s recommendation is explicit: where chlorinated isocyanurates are used, levels of cyanuric acid in pool water should not exceed 100 mg/l.
That is why it is measured: the stabiliser can have accumulated while the free chlorine reading still looks normal, and only a separate analysis shows it.
The Turkish swimming pool regulation likewise defines cyanuric acid as a separate parameter in Annex 1 and requires it to be checked in pools where stabilised chlorine compounds are used for disinfection.
What does this mean for the operator?
Measuring cyanuric acid is the one parameter that tells you when the pool water needs partly refreshing. If the result is rising, adding more chlorine is not the answer — a water change is.
Cyanuric acid is therefore read together with the pool’s microbiological results: if Pseudomonas aeruginosa or the total colony count is rising while free chlorine looks normal, the stabiliser level is one of the places to look.
What the regulation says
In the chemical annex of the pool regulation the upper limit for cyanuric acid is 100 mg/L — the same figure as the WHO recommendation. The annex notes that this parameter is measured only in pools disinfected with stabilised chlorine compounds.
The regulation also states that stabilised chlorine compounds may be used only in outdoor pools. Detecting cyanuric acid in an indoor pool means a product that should not be in use has been used.
Sources
- [1] Guidelines for Safe Recreational Water Environments, Volume 2: Swimming Pools and Similar Environments — Dünya Sağlık Örgütü (WHO) (retrieved 1 September 2026)
- [2] Regulation on the Health Principles and Conditions Applicable to Swimming Pools (Official Gazette, 6 March 2011, No. 27866) — Resmî Gazete (retrieved 31 August 2026)
- [3] Regulation on the Health Principles and Conditions Applicable to Swimming Pools — Annexes (Official Gazette, 6 March 2011, No. 27866) — Resmî Gazete (retrieved 6 September 2026)
The medical and legal information in this article is taken from the sources listed above and is not diagnostic or treatment advice. Figures are reproduced as published in those sources.
