Yellow Stains

Yellow Stains In Pool - What Could They Be?

Yellow stains in your pool are unsightly and often lead to the impression that your pool is dirty. There are a couple different causes of yellow stains in a pool, with each of these causes requiring a varied approach to stain removal.

Read on to learn more about the different causes of yellow stains in pools, as well as what approach we recommend to remove your specific type of stain.

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Causes of Yellow Stains

Before treating your stains, it is necessary to rule out other causes of yellow patches on your pool’s surfaces. Pool owners may mistake the signs of yellow mustard algae infestations for stains.

This algae appears as yellow or brown patches along the surfaces of your pool. Yellow stains in your pool that are not attributable to active algae growths are either caused by organic matter or iron oxidation.

Organic matter stains are typically caused by the leftover remnants of a now-dead algae infestation or from broken down pieces of larger natural debris such as leaves or grass clippings that have blown into the pool.

These stains are easy to identify with a scrub-test. To perform one, simply scrub the yellow stain in question with a stiff brush. If it budges, the stain is organic.

If the yellow stain shows little to no change during a scrub-test, you most likely have metal staining. Dissolved iron is the most common cause of yellow stains in a pool, and iron stains can also contain traces of orange and brown, similar to rust.

Treating Yellow Stains

Yellow stains in your pool that are showing up due to the presence of mustard algae should be dealt with using an algaecide product such as Lo-Chlor Algae Knock Out.

This product is effective on invasive algae strains and does not have negative effects on your pool’s chemistry. After treating your pool with an algaecide, scrubbing effective areas should easily remove yellow patches of dead algae.

You could also use the Lo-Chlor Multi Stain Remover to reduce the amount of scrubbing you need.

This product also works to remove other types of organic stains that we discussed earlier, and is effective on multiple metal stains. It can be used as an all-over treatment or a spot treatment, and is also effective at future stain prevention.

If you have identified that your problem is iron staining specifically, you may want to use a stain remover designed for iron buildup.

If you are unsure about the type of stain you are treating, it is best to go with an all-purpose stain removal product to increase the likelihood of positive results.


Yellow stains in a pool can be caused by algae, organic debris, and even iron metal staining. Although there are a variety of causes, each cause has a simple solution once you have determined the source of your yellow stains.

Overall, the easiest way to remove most yellow stains is by using a stain removal product designated as all-purpose, meaning that it works on both organic and metal deposits that form on the surfaces of your pool.

Do you have any questions about yellow stains in your pool? Leave us a comment down below!

Louis from Pool Advisor


A chemical engineer by trade, Louis is committed to debunking myths in the pool industry by explaining the underlying chemistry and making it accessible to all.