Pool Blankets & Covers.... Warning


In some locations pool covers have become mandatory to help with water conservation and minimise evaporation. Whilst this makes sense, it can also cause issues for owners of fibreglass pools and pools with vinyl liners.

All pools require oxidisers as part of the sanitising process. The most common pool oxidiser is chlorine which is added manually or automatically via salt/mineral chlorination or auto dosing pumps. Chlorine is a gaseous chemical which quickly dissipates to the atmosphere and at levels used for pool sanitation it is not usually detrimental to the pool surface. However, when a pool cover is added this holds/traps the oxidiser in the water and the chlorine levels can very quickly increase to the point they will bleach fibreglass gel coats and vinyl liners. This commonly happens during periods of winterisation when checks and balances are often forgotten or ignored. We have heard of salt/mineral pools with chlorine levels in the 10 - 15 parts per million (ppm) range which will likely & rightly void any warranty from your pool or liner manufacturer.

pH control is just as important! High pH levels alone can also cause gel coat fading, pH balance is important to protect gel coat and manufacturers warranty. Operating a high pH for prolonged periods should be avoided.

Our advice if you use a pool cover is to remove it periodically to allow the water to “breath” and check your chlorine & pH levels weekly and adjust accordingly. Enviroswim is no different in this respect, although we only produce minimal chlorine, over time it could reach damaging levels if the oxidiser output is not reduced to compensate for the pool cover. 


Typical salt/magnesium/chlorine pool recommend chlorine levels, 1 - 3 ppm


Enviroswim system 0.2 - 0.4ppm 


If your levels under the cover are higher than recommended reduce the oxidiser output, daily run time or both until safe residual levels are maintained along with good pH control.

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