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Why do I have a stain?

Stains are fairly common in swimming pools & getting rid of most of them is quite simple, but there are a few that can be a bit more challenging. 

What is it?

The main way to help determine the source of the stain comes from the colour. Have a good look at it’s colour to narrow down the possible cause. Most stains will fall into either metal or organic based categories and these have a variety of colours. 

Organic Staining:

Mostly caused by algae, leaves, twigs, berries or even dead animals (worms, frogs etc.) – in fact anything organic that falls into the swimming pool and is allowed to settle on the bottom to decay. So, prevention is to get any of these things out and off the bottom of the swimming pool as soon as possible. The good thing about Organic Stains is that they are quite easy to remove. If it is organic, you may be able to see debris on top of the stain.

Greenish / Brown is usually caused by leaves, twigs or mud.

Red / Blue is most likely to be berries or seeds. 

Metal Staining:

Metal / Mineral stains may be caused by corrosion of swimming pool equipment due to bad chemical maintenance or the water that has been used to fill the pool. The metal is released from the water and will cling to the swimming pools’ surfaces and appear as staining. The prevent this from happening there are products that will keep the metal in the water therefor enabling it to be filtered away. If you already have stains then you may be able to identify if it is from a metal and which type of metal by looking at the colour of the stains – although these stains have a wide spectrum of colours, a few are more common…

Dark Reddish / Brown or a Rusty appearance is usually caused by metal.

Green, Blue or Black is usually caused by Copper.

Rusty, Brown or Green / Brown patches is caused by Iron.

These are often caused by the chemical balance in the swimming pool not being properly maintained. Low pH combined with high chlorine can cause erosion in the pools heater, not only damaging the heater but also leaching Copper and other metals into the Swimming pool.

Brownish / Black or Purple is caused by Manganese. You will need to check that the water going into the swimming pool i.e. tap water or well water etc. is not the cause of the problem. 

One way to see if it is a metal stain is to place a Vitamin C tablet in a sock and put it on the stain – if it removes the stain then you know that it is caused by metal and you can then treat the swimming pool with Ascorbic Acid (Vitamin C). To treat the pool, you will need to lower the chlorine level in the water to as near zero as possible as the chlorine will eat up the Ascorbic Acid before it can complete the job of removing the stains from the swimming pools’ surfaces. 

Water Sample:

If all of this proves too difficult for you, then take a water sample from your swimming pool into our Pool Shop and we will be able to do a full analysis on it. Make sure that the container that you use for your water sample is clean. Hold the container upside down and push it completely under the water, as near to the middle of the swimming pool as possible, turn it the right way up and let it fill. Don’t take a sample from near a jet, inlet or the top few inches of the waters’ surface.

We carry a range of products to cope with metal stains. You will however need to find the cause of the stains as the products will only cure it if the source of the staining has been dealt with.

Removing Organic Staining:

The First thing that you will need to do is to skim and vacuum the swimming pool, as well as brush the sides and bottom well, in preparation for the stain removal.

If you have a Plaster, Concrete or Tiled Swimming Pool you can check if it’s an organic stain by pouring chlorine directly onto the stained area – leave it for a moment and then brush vigorously. You should see the stain start to disappear. You may find that it is successful with just one application, but if it is stubborn the repeat the process until the stain has been fully removed. If you have multiple stains, then you can treat them in one shot by “shocking” the pool water – this entails adding a very high dose of liquid chlorine to the water (it will take 48hrs to burn off). The more you brush the stains, the more it will help the “shock” to work on them. After the 48 hrs is up, check all the chemical levels of the water and re-balance if necessary.

 *Do NOT pour chlorine directly onto a stain if it is a Vinyl Liner as it will bleach the vinyl*