Copper Stains in a white plastered pool

28th May 2020 Off By RiddsAquaCentre

I received a phone call from one of our clients, he said that he had an emergency, his pool had turned black overnight.
Some black marks were noticed a few days before and dismissed as black algae forming, the treatment of which is relatively simple, simply add an algaecide containing Didecyl Dimethyl ammonium chloride, in as high a concentration as you can find, (Africhem Algaecide Extra Strength is a good example).

I have added some pictures so you can see the extent of the staining. The pool pictured was white before the stain.

What Caused this Stain?
The stain was caused by the copper in the water, as there was an abundance of rain in the days preceding the stains the pH and water balance was out. This caused the copper to come out of solution. The client added chlorine which oxidized the free copper and the stains resulted.

What were the warning signs?

What normally precedes this kind of severe staining is that the water appears to be turning green, this is actually the start of the copper oxidising.
Think of the copper arm bands that some people wear, there is a green to black stain on the wearers wrist, this is the deposit of copper on the skin. Exactly the same will occur in the water, you can easily tell the difference between a green pool due to algae, because the water will become turbid with algae growth and in the case of copper the water will remain very clear.

What can I do do to prevent it?

Prevention is better than cure. Be aware of what you are adding to your pool water. Look at the active ingredients on the label of the chemical you are about to use. they must notcontain any heavy metals such as copper and zinc. these metals do kill algae very well but they also cause these kinds of stains.
If you suspect that the water may have traces of these metals, have the water tested for copper.
Do not add oxidising agents such as Chlorine, Bromine or Peroxide in the presence of copper as this will accelerate the staining.
If you have metals, you can easily treat by adding a metal remover.

What can I do to remove the stains?

I wish I had an easy solution here, but unfortunately the stains are irreversible. Think of the stained streak often found under a dripping hot water tap in your bath or basin, that stain is impossible to remove. So it is in your pool. the only solution is to resurface the pool.
To avoid this unnecessary expense, do not use copper sulphate products!

Is there another way that copper can enter my pool?

Yes, through the source water. It is always a good idea to have your source of water tested before using it to fill a pool, this will not only give an indication of metals present, but also better prepare you for the maintenance of your pool in the long run.

Ar Ridd’s Aqua Centre we are more than equipped to help you deal with these problems should they arise. If you suspect anything like this could be a problem for your pool, don’t hesitate too long, get it sorted out straight away. Go to to find a dealer or to contact us.