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Chlorinated lsocyanurates and Chlorination Summary

Chlorinated lsocyanurates

(Stabilized Chlorine)

This family of chemicals is in wide use for swimming pool chlorination. The family is composed of sodium dichloro-s-triazinetrione and trichloro-s-tria zinetrione – chlorine compounds that contain cyanuric acid (stabilizer). The dichlor is more soluble and provides 56% or 62% available chlorine, depending on formulation. dichlor provides 90% available chlorine and is used when a slow release of chlorine over a period of time is desired. The dichlor compound has little effect on pH, while trichlor is extremely acid (pH 2.8 -3.0). Dichlor can be added directly to the pool; trichlor is generally fed through an erosion-type feeder, but never through the skimmer basket.

The major effect of cyanuric acid on hypochlorous acid (HOCI) is to keep it from being decomposed by ultraviolet (LTV) light such as contained in sunlight.

Because it is readily decomposed by LTV light, the dosage of a chlorinating agent that is sufficient for an indoor pool is dissipated rapidly in an outdoor pool. Cyanuric acid bonds with the available chlorine in a manner that does not use up the chlorine. At high stabilizer levels (over 100 ppm), chlorine’s efficiency may be reduced. The operator should consult the local codes and manufacturers’ recommendations on the proper use of stabilizers.


Chlorination Summary
– Chlorination both sanitizes and cleans the water by oxidizing organic impurities.
– A free chlorine residual of 1.0 -3.0 ppm is preferred. Combined chlorine should not exceed 0.5 ppm and may be destroyed by breakpoint chlorination.
– Proper pH control (7.2-7.6) provides better chlorine efficiency.
– When cyanuric acid is used in an outdoor pool, chlorine consumption is reduced, because the chlorine degradation caused by LTV light is reduced.
– There are many chlorinating agents available but each provides HOCI, the active chemical specifically for disinfecting.