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Help! My Pool is stained

Stains are a fairly common problem in Swimming Pools. There are different types of staining that can occur, all with different causes. All stains can be removed, some simpler than others! Firstly, you need to determine the source of the stain to narrow down the possible cause. Have a good look at the colour of it, most stains will fall into metal or organic based categories and have a variety of colours. 

Metal staining can be caused by corrosion of Swimming Pool equipment due to chemical imbalance, in particular the Pool’s heater which not only damages the heater itself, but also leaches Copper and other metals into the water. Stains can also be caused when topping up a Pool if spring water is used as spring water has a high mineral content. To prevent this from happening, there are products that remove metal from the water. Common colours for metal staining are;

Dark Red/Brown or rusty – caused by metal.

Green, Blue or Black – caused by Copper.

Rusty red/brown or green/brown – caused by Iron.

Brownish-black or purple – caused by Manganese.

What to do

In preparation for the stain removal, give the bottom and sides a good brush and skim and vacuum the Pool.

We carry a range of products to cope with metal stains however, you will need to find the cause of the stain to determine which product is best to use. You will also need to deal with the source of the stain to prevent staining from reoccurring.


Organic staining is mostly caused by Algae, twigs, leaves, berries or even dead animals (worms, frogs etc). Anything organic that falls into the Pool and is allowed to settle on the bottom to decay. With organic stains, you may be able to still see the debris on the top of the stain. To prevent organic staining, simply remove any debris from the Pool as soon as possible. Common colours for organic staining are;

Green/brown – caused by leaves, twigs or mud.

Red/blue – caused by berries or seeds.

What to do

In preparation for the stain removal, give the bottom and sides a good brush and skim and vacuum the Pool.

If you have a Concrete, Plaster or Tiled Swimming Pool, you can check if it’s an organic stain by pouring Chlorine directly onto the stained area, leaving it for a moment and then brushing vigorously, you should see it start to disappear. One application may be successful but if it’s a stubborn stain, then repeat the process until it has fully been removed. If you have multiple stains, then you can treat them all at once by ‘shocking’ the Pool. This is done by adding a high dose of liquid Chlorine to the water (this takes 48hrs to burn off and the cover should be left off and no swimming during this time). The more you brush the stains, the more the liquid chlorine will work. After the 48hrs, check all the chemical levels and adjust if necessary.

If you have a Vinyl Swimming Pool, ‘shock’ the whole Pool as above. Do not directly pour Chlorine onto the stain as it will bleach the Vinyl.

Alternative to the above, you can take a water sample from your Pool and bring along to us (or your local Pool Company) to carry out a full analysis of it. Use a clean container and try to take water from as near to the middle of the Pool as possible. Don’t take a sample from the water’s surface or from near a jet or inlet as this can provide a false reading.