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The following Technical Information Bulletin is a re-write of a US document originally prepared by Dawn Marie Teany and Kim Click (Technical Information Services, Bio-Lab, Inc., Decatur GA) on 28 July 2000.

By definition, "scale" is simply any solid material that precipitates out of solution and settles or adheres to pool surfaces, fittings, lights or equipment. Based on laboratory analysis, the most common form of scale observed is that of calcium carbonate. As it forms, other ions or particles (such as metals or organic material) may be trapped into the scale matrix and colour the scale. Pure calcium scale is white, but colours such as tan, grey or blue have also been observed.

As much as we try to prevent scaling, not all deposits of calcium are avoidable. Water is commonly known as the universal solvent for good reason. Given enough time, increased pressure and/or temperature, water will dissolve most minerals. That being said, the most common cause of scaling is simply improperly maintained water balance, with total alkalinity, pH and calcium hardness being vitally important factors in the formation of calcium carbonate scale. Water temperatures also play a significant role in scale formation.

Importantly, scaling can occur due to improperly winterised, covered pools, particularly where there has been little or no water flow for prolonged periods of time. How then can scale formation be prevented prior to winterisation? Based on trends observed over the past few years, pools indicating a strong tendency for pH increase over the winter months more readily experience scaling at the opening of the swimming season. With the pool being covered, this is most probably due to the lack of exchange between dissolved carbon dioxide in the pool water and the atmosphere. Whilst we cannot pinpoint the exact cause of every scaling incident, Bio-Lab does suggest the following closing advice for all white plaster, coloured plaster and concrete pools:

1. Adjust the pH to the lower end of the acceptable pH range (7.4 - 7.6).
2. Apply BioGuard Scale Inhibitor at the rate of 250 mL per 10,000 litres. Do not worry about overdosing as it will not be detrimental in any way, and will simply continue to provide excellent protection for the pool surface.
3. Minimise the time the pool is kept covered as much as possible. This may mean closing later in the autumn and opening earlier in the spring, or it may mean removing the cover on a periodic basis during the winter. This will minimise the time the covered pool is subjected to warmer water temperatures and allow for exchange of carbon dioxide with the atmosphere.

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.