Salt Water Swimming Pools

Introduction to Chemical Treatment

Swimming pools in the early days were of the fill and empty type. This consisted of filling the pool at intervals of approximately two weeks and when it became grossly polluted, it was drained out and refilled with fresh water. The first pool using filtered water and chlorination in Australia was recorded in Wickham Street Brisbane followed by the Tattersalls club pool in Sydney in 1924. Followed by the Y.M.C.A. building in Melbourne in 1925 and in 1926 a tender was accepted for chlorination and filtration of the Melbourne City Baths. However, these pools operated on marginal chlorination. The modern treatment of swimming pools was introduced in England about 1950 and was mainly due to the work done by Palin with the understanding of chloramine formation and breakpoint chlorination. This was followed up in 1953 by Burgess, Burns and Tidy of the London County council in converting pools under their control to breakpoint conditions. In Australia, it was not until about 1957 that modern treatment methods' were introduced into public pools, and now there are very few public pool operators who do not have some understanding of the basic principles involved. However, private swimming pools operation has lagged far behind that of public pools, and it is only within the last few years that the general standard has risen. Because there is no organized system of training, there is still a lot of secrecy in the chemical treatment by service operators of swimming pools, and even though an operator may be knowledgeable he still gets into difficulties.

Purpose of Chemical Treatment

The chemical treatment of private pools is basically the same as for public pools.

The aims in water treatment can be broadly listed as follows:

• To sterilize the water in order to prevent the spread of infectious diseases, and others that cause sore throats, earaches, etc. also parasites that cause ringworm, etc., can be destroyed.
• Prevent algae growth formation.
• Eliminate odours and obnoxious tastes.
• Prevent irritation to eyes and mucus membranes.
• Prevent Scale formation.
• Keep the water clear, attractive and sparkling.
• Prevent corrosion to fixtures and fittings.

Basic Requirements of a Swimming Pool

To achieve these previous aims a pool must be properly designed and have certain basic requirements.

1. A pump with a circulation rate sufficient to give a minimum 6 hour turnover for the larger pools used for motels and schools. Small pools with very light loadings can achieve satisfactory results with longer turnovers, up to 12 hours.
2. A lint catcher to remove large solids, such as grass clippings, leaves, hair, paper etc.
3. A sand filter or diatomaceous earth filter.
4. Scum gutters should be provided for larger pools of 50,000 - 100,000 gallon capacity.
   For the smaller pools, skimming devices should be used. These are required to remove hair oil, body fats, make up preparations, Sputum etc. which float on the surface of the water and would otherwise concentrate if a take off below the surface is used.
5. The type of circulation is important in the larger type pools. The water should have the shortest travel, ie, in rectangular pools the water should enter the ports along one side of the pool and out over scum gutters on the opposite side of the pool (some old pools the water entered at the shallow end and was drawn off at the deep ending giving the maximum travel).

With the small pools the type of circulation is not so vital because of the light loadings. However odd shaped pools have to be considered on their merits.

With small pools, hand dosing at night is generally practiced, whereas with larger pools with heavier loadings, facilities for continuous dosing of chemicals are necessary to maintain good conditions.

Factors Effecting Chemical Treatment

The principle of treating swimming pool water is similar to that of town water supplies in so far as clarification is carried out by settling and filtration, in the case of sand filters, normally with a flocculation using alum.

This is then followed by disinfection using chlorine, to kill harmful bacteria and to eliminate tastes and odours.

However, town water has only to be treated once, while swimming pool water requires more exacting treatment because it is continually going through a cycle of purification and re-pollution at various levels due to the number of bathers in the water.

The amount of chemicals required to treat the water to a safe standard, ie good drinking water, will vary with the following factors:

1. The volume, depth and condition of the water in the pool
2. Type of circulation and turnover
3. The number of people using the pool, also the age and sex
4. Weather conditions
5. The environment ie, subjects to wind blown leaves or grass clippings etc
6. pH level
7. Temperature of the water
8. The type of chemicals used