DECHLORINATION WITH SODIUM THIOSULPHATE Swimming pool over chlorination can occur because of automatic controller system failure or operator error, but the real problem comes in rectification. The method preferred and recommended is one of dilution until bathing conditions become acceptable, a second and emergency method only, is to use sodium thiosulphate. In comparison with the process of dilution, this is a relatively inexpensive method of solving the problem and is therefore often used. If the use of sodium thiosulphate is necessary it is extremely important not to overdo it. The addition of too much will create the opposite problem of not being able to establish a chlorine residual at all. Further information on hth can be found in the hth Pool Manager's Handbook obtainable from us by request via the Contact us page ---------------------------------------------------------------- FLOCCULATION > Sodium aluminate > PAC (Poly Aluminium Chloride) > Alum (aluminium sulphate, kibbled alum) (All the above are flocculants) A flocculant is a material used to aid filtration and is often referred to as a coagulant. It is especially good at removal of micro organisms not made harmless by disinfection i.e. Cryptosporidium and Gardia. Flocculants work by bringing the micro organisms and particulate matter out of solution as solids (coagulation) and then bringing the solids together (flocculating), which is easier to trap on a filter. These entrapped particles on the top of the sand bed are discarded during a backwash operation after which the flocculant will need replacement. The ideal method to replace the flocculant is to dose via a metering pump. Further information on hth can be found in the hth Pool Manager's Handbook obtainable from us by request via the Contact us page ---------------------------------------------------------------- HYGIENE Hygiene The importance of maintaining clean, sanitary conditions around the poolside is widely recognised. However, pool managers must appreciate that any product or compound which is used to clean pool sides and surrounding areas, may ultimately mix with the pool water, particularly in the modern 'deck level' pool. Modern industrial cleaning formulations are very efficient in the removal of dirt, grease and scale, but are not necessarily designed specifically for use in a swimming pool. These products could for instance be incompatible with the pool chlorine donor or may cause loss of clarity, foaming or precipitation of insoluble residues. Products used for cleaning pool areas should be bio-degradeable or preferably, be designed for use in pools and rigorously tested by the manufacturer. Listed below are some of the ingredients that are often found in cleaning products and the possible effects they could have in pool water. ---------------------------------------------------------------- NATURAL SOAPS (e.g. sodium palmitate and sodium stearate) These will interact with hardness salts in pool water causing cloudiness and the formation of insoluble soap scums such as calcium stearate. Soap will remove dirt, oils and body fats from filters and could cause foaming of pool water. ---------------------------------------------------------------- SYNTHETIC DETERGENTS Modern detergents are available in a variety of chemical compositions and properties, resulting sometimes in the following effects when they are allowed to mix with pool water: > Foaming, particularly at pool water inlets or in the wake of bathers activity > Removal and suspension of dirt and body fats from filters and bathers, giving cloudy water > Chemical reaction with the free chlorine residual – bubbles may be observed, or a milky effect local to the mixed products maybe apparent > Eye or skin irritation to bathers, resulting from chemical reaction between nitrogen based detergents and the free chlorine residual. This can occasionally be detected as a high combined chlorine reading with the DPD test ---------------------------------------------------------------- SILICATES (e.g. sodium metasilicate) These will slowly and continuously form insoluble silicates, causing cloudy pool water, due to a chemical reaction between hardness salts. Silicates are designed as suspending agents for dirt and consequently they may impair the efficient operation of filters. Silica, which is used as an abrasive, will also cause clouding of the water. Where silicates have been used in large quantities, they will impart an oily feel to the water. ---------------------------------------------------------------- AMINES (e.g.triethanolamine) These are often incorporated in alkaline degreasing products. Amines will react with a free chlorine residual, giving chloramines. Chloramines formed in this way may cause skin and eye irritation and may not necessarily be reduced by breakpoint chlorination. ---------------------------------------------------------------- PHOSPHATES Phosphates are known to promote algae. ---------------------------------------------------------------- PIGMENTS AND DYES Could cause possible discolouration of pool water, particularly in deep areas. ---------------------------------------------------------------- MINERAL ACIDS These could etch tiles, remove grout or damage marbleite and other surfaces if used too liberally or solution is too strong. ---------------------------------------------------------------- ESSENTIAL OILS These are usually added to simply add fragrance to the cleaning compound. It is possible that a reaction with the chlorine residual could occur giving varying effects. ---------------------------------------------------------------- ADVICE NOTES 1 Insist bathers use the pre-swim cleanse facilities 2 Restrict the use of outdoor shoes coming into contact with the poolside 3 Wash the poolside regularly with water from the pool. If stronger sanitisation is required use a weak proprietary product 4 Deposits of body fats, either on the poolside or on scum lines can be removed by cleaning with an aqueous solution of sodium bicarbonate or sodium carbonate 5 Use products from a reputable supplier, preferably formulated specifically for use in pool areas 6 Follow instructions on the container. Dilute to instructions stated 7 Follow all safety and handling guidance 8 Never mix chemicals of any kind or brand
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