What are the pink marks on my liner?

It does not happen very often, but sometimes a pool liner will display some pink coloured marks. These are usually on the floor of the pool and will look “cloudy” rather than have defined lines or shapes. The pink colour is more commonly seen on a liner that has a white base and it is what we call “microbial staining”.

It seems to affect about 1 in every 500 pools, so while it is uncommon, it does happen. What causes it? Following heavy rain, pools in an area with a high water table can get water pass behind the liner. If this water contains certain microbes, and these microbes feast on the nutrients in the water, they will excrete small deposits. Those ‘deposits’ are acually a dye, and these dyes can move through the PVC and create cloudy stains on the inside of the pool liner.

This problem is purely site related and has no relationship to the batch of pool liner fabric or the colour of the liner or the person who installed it in the pool. It just happens when the ground water brings with it these nasty microbes, who in turn discolour the liner.

The good news is the liner is not affected in performance or longevity. The dye has just changed the colour a little and the pool will remain fully functional and easy to maintain as always. The microbial staining can disappear after short while if the ground water drains away from behind the liner and the stain will slowly fade.

Be careful if your pool chemical supplier advises you to “double the dose” of chlorine as you can damage the pattern or colour of your pool liner. (While this technique has been known to reduce the stains, it is most certainly not recommended).

A product called “Copperas Iron Sulphate” has been suggested as a remedy for this problem and is a much better option to try.

Apply the Iron Sulphate by using around 5Kg’s for an average 9mx4m pool. It is applied by sprinkling it around the pool surround (on all sides) and then watering it well into the ground with a sprinkler. Allow it to soak in and get down to the ground water around the pool over the next few days. This process is designed to change the ground PH to a level that will kill off the microbes and stop the dis-coloration of the pool liner. Be careful not to get the Iron Sulphate on paving areas as it can stain concrete and other paving products.

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