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What to do if your pool turned green during lockdown

Owners arriving later than usual at holiday homes, as European travel restrictions lift, may have the bad experience of finding their pool has turned green.

Tips from a pool expert

Swimming pool expert Alexander Pearson, of Gaius Terra & Aqua pool installers in the south west, said there are basic steps which many people will be able to carry out themselves. He said: “You only need to drain the pool if the water is really thick and smelly. Otherwise, it is just a waste of water and you risk structural damage to the pool.”

What to do

You should first switch off the pump, close all the valves, empty the pump basket and then put it back. After that, clean the pool as well as you are able to, using a net to remove large objects, and a brush for the walls. Empty and clean the skimmer basket and put it back, and also clean the pool cover, especially if it has slats, making sure there is nothing between them. Then put in a 35% solution of hydrogen peroxide (sold as Oxygène Actif).

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For most garden pools, five litres will be enough, although larger pools might need more. Set the six-way valves on the treatment unit to recirculation and restart the pump. The water should start to clear in 24-48 hours.

When it is clear, backwash the filter if you have one – salt pools do not usually have a backwash. You then need to balance the water using the instructions which came with the pool, first checking the titre alcalimétrique complet (TAC), a measure of pool salinity, then the pH or acidity level and finally, the amount of chlorine, if you have a chlorine pool.

Salt pools

If you have a salt pool, obviously check the salt concentrations. Then set the filter for normal operation. “The use of hydrogen peroxide, I have found, is the best way,” said Mr Pearson. “However, every situation is different, and if you are unsure, it is always best to call in a professional pisciniste.”

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