A Note on the Destruction of Excess Chlorine in Swimming Pools

Chlorine in Swimming Pools P. M. HoLRoyD Department of the Strathclyde Regional Chemist, 14 Beckford Street, Hamilton The destruction of excess chlorine by addirion of either sodium thiosulphate or sodium sulphite has been investigated. Sodium sulphite was established as the preferred reagent. Overchlorination of a swimming pool can occur following malfunction of automatic dosing equipment and failure to detect the problem because of bleaching of the colour in the normal poolside test. If the overdosing is severe the method of partially emptying the pool and refilling with clean water is not satisfactory because (a) There may be environmental consequences to dumping water high in chlorine content. (b) There is an appreciable thermal energy loss to be made up. (c) It can take an appreciable time to partially empty and refiil a large pool. For these reasons the alternative approach of destroying excess chlorine by means of a reducing agent has been investigated. Fimiliarity with the quantitative reaction between sodium thiosulphate and iodine mighi lead one to expect a similar reaction with chlorine, and indeed the HMSO booklet ,,Odour and Taste in Raw and Potable Waters”l states tha