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08 June 2020
Why is my pool water green and how do I fix it?

There is an indescribable joy in having your own swimming pool – there’s nothing like stepping out into the sunshine and gazing at the crystal-clear water beckoning you to take a refreshing dip. But we’ve all probably experienced that one time when we are not greeted with shimming clear water, but a cloudy green haze that looks about as inviting as a bath of baked beans.  Why do pools turn green and what can we do to fix it and to stop it from happening again?

Why is my pool green?
The green discolouration is a reaction to algae growing in your pool; it can grow and spread rapidly, particularly in warm weather. Indeed, on an especially hot day, a mild case can become an algae infection overnight. The algae have most likely grown and spread due to an imbalance of chlorine in the water.

Allowing the chlorine levels to drop for even a day or two can lead to a ‘green pool’ in a short time, so checking the chlorine level frequently is essential.  If it is already too late and the water has turned green, how do you bring it back to normal and stop the algae from returning?

Cleaning the green
Given its most likely a lack of chlorine that caused the algae growth, your first port of call should be to boost the chlorine levels in your pool immediately.

Also, consider supplementing this ‘chlorine shock’ with an algaecide supplement if the problem is particularly stubborn, which you can tell by how dark the water has become.  If the colour is a light green, one shock treatment should be enough to clear it.

Of course, a simple shock treatment may not always be enough. If the  water is a darker, almost black-looking shade of green, it has been left untreated for a long time and will require professional pool treatment. The pool will need to be drained and thoroughly cleaned by a qualified pool service engineer.

Green gives way to blue
Once the algae have been dispersed, you might notice a lingering cloudiness at first. However, once you’ve run the pump and filter for a full 24 hours, you should notice the water slowly returning to normal and you’ll be eager to get back into the pool and make the most of the sunshine.

As for how to ensure your pool doesn’t go green again, the answer is simple – ensure your chlorine levels are always consistent (every day) and regularly test pH and alkalinity levels because chlorine needs the right pH levels in order to do its job effectively and it also needs to be within safe limits.  It’s a balancing act that you’ll be playing throughout the summer months, but with the world on lockdown and record summer heat waves predicted, it’s one that will pay dividends, come July.

The very best care you can give your swimming pool is regular professional servicing. This will ensure that problems are avoided in the first place and any little irregularities are identified by a service engineer who knows your pool and plant room inside out. This avoids small problems becoming big ones that can put your pool out of action.

We have a fuller article, How to Combat Swimming Pool Algae here.

At London Swimming Pool Company we specialise in swimming pool maintenance, servicing and refurbishment. If you have a pool that’s in need of regular maintenance or a facelift, contact us for an initial discussion – there’s no substitute for expert advice. 

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