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For several seasons a phenomena has occurred with some swimming pools. These pools appear "typical" at opening. After initial start up chemicals are added, the follow-up check on sanitiser residual reveals no sanitiser in the water. Repeated additions of shocking compounds do not seem to provide the ability to maintain a residual. Despite the absence of an active sanitiser residual, the pool is clear.


Bio-Lab has recommended that these pools be maintained with the usual sanitation program of the owner with weekly addition of Burn Out or Burn Out 35 shock each week. Some pool owners are uncomfortable with the lack of residual. These owners have chosen to shock with the quantities of chemical product necessary per the Chlorine Demand Test available through a Technical Services analysis of a water sample. Both groups usually have a sanitiser residual by mid to late summer. However, we occasionally find pools at closing time which do not have the ability to maintain a consistent sanitiser residual. How should these pools be closed?


Normal closing procedures should be used as outlined in the pool owners' manuals. When shock is applied, use twice the normally recommended amount. Addition of one and one-half times the usual quantity of algaecide is recommended. This would be 3 bags of Burn Out shock or 5 bags of Burnout 35 shock per 40,000 litres 1.4 litres of Polygard algaecide per 40,000 litres. These steps should provide adequate protection through the winter to allow a normal opening in the spring. For extra protection in white plaster pools only, use a floater. This will provide a continuous feed of chlorine for most, if not all, of the closed months.


In vinyl pools, about mid-winter, a chlorine solution should be poured into the pool water. Care must be taken to pour this into the deepest possible area to avoid bleaching of the liner. This chlorine solution can be made by 1 bag of Burn Out or Burnout 35 in 10 litres of water. Be certain that all granular material is fully dissolved before adding this solution to the pool.


The above information is supplied by Bio-Lab and represents its best interpretation of available technical information at the time of preparation. The sole purpose is to supply factual information to Bio-Lab customers. It is not to be taken out of context nor used as support for any other claim not made herein.