Pool Care Pool Troubleshooting

How to Remove Yellow Stains from Pool Steps?

Pool stains are always a menace. When the yellow stains and spots start to appear on your pool steps, it indicates yellow pool algae might infect your pool, or it has iron deposits. Don’t get me wrong; sometimes, the iron metals can cause brown stains and yellow spots.

Removing these yellow stains doesn’t need magic; all you need is balancing and triple shock your pool water. You will need to brush the algae first to allow the chlorine to act on them from all sides. For iron deposit stains, the best solution is iron stain remover.

Keeping your pool healthy and clean should always be your priority during pool maintenance. You want to make sure your pool looks as inviting as it can be all the time. Here is a guide that will help you get rid of and prevent yellow stains.

What’s causing the yellow stains you your pool steps

As aforementioned, there two major causes of the yellow stains on pool steps. It can either be yellow mustard algae or iron deposits (rare).

Yellow Mustard Algae

It’s also referred to as mustard algae or yellow algae. It’s not a common alga, but you won’t notice it until you start seeing the yellow stains when it finds its way to your pool. It’s pretty persistent that regular doses of chlorine won’t kill it.

When it settles on your pool steps, it creates a slippery substance that makes it challenging and treacherous to climb in and out of your swimming pool.

If uncertain, it’s yellow algae; you can test it by scrubbing it with a pool brush. If it disappears quickly but gets back in few days, then your pool is infected with Mustard algae.

The sad news is, it doesn’t grow inside the pool; it’s introduced. You could bring it in with your swim costume, especially if you swam with the same attire in infected water like the beach.

You can also introduce it to your pool equipment, especially the cleaners. When you store them, they can collect the yellow algae spores and introduce them in your pool the next time you use them.

Another way the mustard algae can find its way to your pool is through strong winds. The winds can blow the spores from other sources and deposit them in your pool water.

Iron Deposits

Metals in your pool? Did you know there are multiple ways you can add metals to your pool unknowingly?

If you use unfiltered well water, you’ll be adding all types of metals the water has collected as it passed through the earth’s natural minerals.

Another way you might be adding the minerals is through the city water. Yes, they do filter some metals but up to healthy drinking standards.

When you refill your swimming pool using the city water multiple times, the metals can rise to concentrated levels.

It can also be through water that drains from the fertilized lawn. If you use a fertilizer containing iron, copper, or other metals, they will be swept by rain water to your pool because of their insoluble state.

When these metals are high in concentration, they form metal deposits that settle on the pool surface. Iron forms yellow or brownish stains that might cause yellow stains on your pool steps and other surfaces.

And unlike algae, the iron deposits are stubborn; they resist scrubbing. You will need to add more effort to remove them. A simple test using a unique metal testing solution can help you confirm high iron concentration in your pool water.

How to remove the yellow stains from the pool steps

Have you confirmed the cause of the yellow stains on your pool steps? Is it mustard algae or iron mineral? Whichever the course, here are the steps to follow to get rid of these stains once and for all.

Getting Rid of Mustard Algae Stains

Understand the best treatment for algae is chlorine. That means you will need to add chemicals to your pool water to control the algae.

Wear Protective Gear

So, before you can start, get yourself a pair of chemical-resistant gloves and goggles. Don’t forget to wear a mask and an apron too. The safety gear will protect you from the harsh chemicals you’ll add to kill the mustard algae.

Brush and Vacuum the Stairs

The next step is to brush and vacuum your pool steps. Take the appropriate pool brush for your pool and brush off the algae from the stairs. It helps expose them to the sanitizer.

You can also vacuum the pool; manual vacuuming is the best as those automatic models might skip some spots.

Remember to set the filter to waste when vacuuming. You don’t want some mustard algae to remain in the pool return line.

Balance Your Pool Water

After brushing the pool stairs, be sure to test and balance the pool water. At this time, you can be confident your pool chemistry needs balancing.

You can use test strips, a liquid test kit, or get a reliable digital pool test kit. You can also take a water sample to your local pool store for more accurate testing.

Once you get the results, adjust the chemicals accordingly. It’s necessary to keep the chlorine stable and allow it to have the best effectiveness.

Shock Your Pool

Killing and controlling normal green algae requires an algaecide and a standard dose of pool shock. But when it comes to mustard algae, you have to go an extra step as it’s resistant to both algaecide and chlorine.

The best way is to triple the standard pool shock dose. Typically, you’d need 10-30 ppm of chlorine to kill algae blooms, depending on your algae severity.

So, if you were to triple this, you’d need 30-90 ppm chlorine to deal with the mustard algae. You can also add a chlorine accelerator boost.

It improves the chlorine effectiveness making it more potent to kill severe algae types you may have in your pool.

You can find more on how to shock your pool here.

Remember to shock your pool during the night since sun rays have a significant effect on chlorine; they can reduce the treatment effectiveness.

Allow the pool filter and pump to run for at least 6-hours to allow distribution of the pool shock. Once the wait is over, balance the water chemistry.

Getting Rid of Iron Stains

When correcting the iron stain problem, you can start by lowering the chlorine levels to 0 ppm. You’ll also need to lower the pool pH to around 6.8.

Add an iron stain remover to the pool steps to help loosen the stains up for easy brushing. You can now add a quart of an iron remover or metal Sequestrant for a 5,000-gallon pool after this.

You can now leave the pool to rest overnight. The next day, raise the water pH to anything above 7.2 and below 7.8.

When done, balance the other water chemicals and give your pool the regular pool shock. You can vacuum out the iron particles on the pool stairs and floors.

How to prevent yellow stains in your pool

The stains are gone, and your pool steps are clean again. Will they remain clean? How do you prevent the stains from coming again? The best solution is to deal with their source. You will be able to keep your swimming pool looking beautiful and save you from all the extra work required to remove them.

Preventing Mustard Yellow Stains

Here are the steps you can take to prevent mustard algae from growing in your pool again.

Wash Your Bathing Suits

When you use your swimming suits in other waters like the beach, make sure you wash them right with strong fabric bleach. It will help kill the mustard algae spores that might have stuck on them.

Clean Your Pool Equipment and Accessories

Before and after cleaning using your pool accessories and equipment, be sure to wipe them with some bleach to remove the algae and other contaminants.

Some of the mustard algae can be brought into your pool through these accessories and equipment. Cleaning them makes sure they don’t end up in your swimming pool.

Frequent Pool Filter Cleaning

Another route the algae can take to come to your swimming pool is through the filter. Dirty filters can reintroduce this nasty bacteria. Frequent cleaning of your pool filters can help keep them at bay.

Keep Your Pool Balanced

Like any other algae, it’s harsh for the yellow algae to grow in a balanced pool. Keeping your pool chemistry, especially pH and chlorine balanced, can help inhibit their growth. It’s also a necessary step if you refill the swimming pool with well water.

Skim Your Pool Often

The algae particles can also cling to the tree leaves and other debris. When they fall into your water, and you allow them to sink, the algae can start to grow, and before you know it, it has spread.

Removing the debris as soon as it falls in your pool water would help a lot. You can even invest in a leaf net that can help in trapping the leaves before they get to your water.

Preventing Iron Yellow Stains

If your pool steps weren’t stained by mustard algae but rather by iron deposits, here’s are more vigilant and preventing steps to help you prevent it from happening again.

Invest in a Hose Filter

A hose filter helps filter out any metals found in the water. You can use it to make sure the water you use to refill your pool is clean and free of these metals, including iron, the culprit of the yellow stains. You can even use it with well water, and you don’t have to think of these minerals getting to your water again.

Use of Metal Sequestrant

Metal Sequestrant is a chemical designed to bind the metal particles to prevent them from settling on your pool surfaces. It makes it easier for the filters to remove them.

Keep your pool pH balanced

Maintain a balanced pool pH all the time. When it drops, the acidic water formed can start to corrode the iron metals in your pool, and the deposits will start settling in your pool.


Pool step stains are either caused by mustard algae or iron deposits. Mustard or yellow algae is rare, but it exists. It doesn’t look like normal algae, but it loves to stick to things. With its source being outside the pool water, you can control it by cleaning your swimsuit, wiping down your pool equipment and accessories, and skimming your swimming pool more often. Iron is another thing that can lead to yellow stains on your steps. Preventing it requires you to filter the water you use to refill and balance the pool pH.

About the author

Sharif Miah

Hi! I'm Sharif, the founder of Globo Pool® and I have been working in the pool & hot tub industry for the last few years. I love to share my experiences with people & hope you are enjoying my information and lessons!

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