Re-opening your pool in the spring: how should you deal with green water?

When you are getting ready to re-open your pool, you notice that the water is green: don’t worry, the situation can be rectified. Read our advice on restoring clear water and start to enjoy your pool as soon as possible.

Why is the water in my pool green?

If your water has turned green, this is likely to be because you have re-opened it a little too late. In fact, for efficient re-opening, it is advisable to start up your pool when the water temperature is around 12 to 15 °C. If you open it too soon, you will use up a lot of energy maintaining the water at the right temperature. It’s best to re-open just before the warm weather arrives, because, if the sunrays nurture your pool, while it is still in its winterizing state, algae will begin to propagate…

First stage: cleaning.

Clean your pool basin. Your first instinct will surely be to want to empty the water from your pool: you should know that you don’t need to do that. Begin by using a pool net and removing the largest impurities. We advise you not to use your pool cleaner at this stage because you may damage it. Lastly, brush the walls manually in order to remove any remaining algae.

Second stage: water treatment.

Now, check the water parameters: stabiliser, complete alkalimetric title (CAT) and pH. If the level of stabiliser is high (above 50), it is advisable to drain part of the water and to replace it with water from the network. A correct stabiliser is around 20. Once the stabiliser has been corrected, readjust the CAT. If it is too low, you will not be able to maintain a correct pH. The pH should be between 7 and 7.4: if this is not the case, you are going to need to correct it. The pH can be low after heavy rainfall that may be slightly acidic.

Once these 3 parameters have been adjusted, one single solution will be effective in cleaning your water whether you treat it with chlorine or using a salt chlorinator: shocking it with chlorine. This should preferably be done in the evening for maximum effect.

Firstly, clean your filter then run it continuously.

If you use a sand filter, don’t hesitate to add a flocculant into your skimmer to accelerate water purification: take note of all the tips you can to improve the process!

Why is the water still green in spite of all this?

There are other explanations for why pool water can turn green: a filtration problem, scaled piping, excessive phosphate levels or even a badly-cleaned pool.

Take note of a few specific details for pools filled with water from a well or a borehole. This is raw water, meaning it is untreated, in comparison with water from the network: it therefore requires more treatment. This water can also contain metallic elements. If you do not treat it and you use a salt chlorinator, an oxidation phenomenon will take place and marks will appear on the pool basin. If you have no choice other than to fill your pool with water from a well, make sure that you have treated it thoroughly beforehand. If you have the choice, we advise you to use water from the network, which will save you money on water treatment products.

If, despite our advice, your water is still green, contact your pool specialist for an assessment.