Pool Care Pool Troubleshooting

Mustard Algae: Best Way to Remove It from Your Pool

If you’ve started seeing yellow stains and yellow patches on pool surfaces and you’re sure there are no iron deposits in your swimming pool, there is a high chance it’s infected with mustard algae. It’s probably the most stubborn type of algae you will ever have to deal with.

This microbial menace is rare but also persistent. If it is in your swimming pool, the best thing to do is to get rid of it before it starts multiplying. This post is a complete guide to help you understand how to identify mustard, how to get rid of it, and how to prevent it from infecting your pool again.

Let’s get to it.

What is Mustard Algae and Why Should You Be Concerned?

Mustard or Yellow algae is a type of algae that manifests in yellowish, yellow-brown, or yellow-green colors. When inside a swimming pool, it looks more like pollen, dirt, or sand. Sometimes it’s challenging to realize your swimming pool has it until it’s too late. It also lacks the sliminess characterized by other algae – its texture is closer to dirt and most common in southern climates.

Why should you be concerned?

  • Even though it’s not dangerous to humans, its overgrowth has the potential of harboring harmful bacteria such as E Coli.
  • Unlike other algae, it stains the pool surfaces and clouds the water.
  • t’s easy to transfer to another swimming pool as it tends to stick to things such as bathing suits, toys, floats, and pool equipment.

How to Tell If You Have Mustard Algae in Your Pool

Mustard or the Yellow algae has a distinctive yellow color. It can also manifest in yellow-brown or yellow-green. It looks like a dry, powdery substance, which might be why it’s mistaken as pollen or dirt. It prefers shade and still water.

You’re more likely to find it clinging to the pool walls, bottom, or both. However, you could still find it in a swimming pool with enough sunlight and ideal water circulation, especially in those dead spots and crevices. It mostly hides under the ladder, pool lights, or small cracks.

It’s pretty easy to brush or scrub mustard algae off the pool surfaces and equipment; even most people assume they have dealt with the algae problem only to see it return in few days. But since it likes to hide in those hard-to-reach, tiny, and uneven surfaces, they do take little time to grow back.

What Causes Mustard Algae in a Swimming Pool?

Mustard algae don’t grow in the swimming pool. It’s something introduced into the pool water. The bad news is, it’s highly resistant to chlorine’s sanitization effect. It’s naturally found in natural freshwater or saltwater sources. And as I mentioned, it likes to attach itself to things.

So, if you went swimming in mustard algae-affected waters and forget to clean your swimsuits thoroughly, it’s possible to introduce it to your swimming pool. The same goes for swimming equipment; if you use your pool equipment in mustard algae-infected waters and do not clean properly, you might have introduced it in your swimming pool.

How Do You Get Rid of Mustard Algae in a Swimming Pool?

I mentioned that mustard algae are a persistent alga that can keep coming back if not removed properly. You need to clean everything that gets into your swimming pool and clean the swimming pool surfaces right.

Here are the most effective ways you can get rid of mustard algae in your swimming pool.

Wash Your Bathing Suits

The first place to start with mustard removal is to clean your bathing suits. These are the most common source of this stubborn microbial in your pool.

The best way to clean them is to use color-safe bleach. Bleach contains extra disinfectant needed to kill the mustard algae on your bathing suits.

Clean the Pool Equipment, Floats and Toys

Another probable source of Yellow algae in your pool is your pool equipment, toys, floats, and anything that enters your swimming pool.

Take out everything you use in your swimming pool, brush them thoroughly before sanitizing them with bleach or using a bleach-based disinfectant.

The best way is to create a solution and spray it on these items. You want to mix ten parts of water with one amount of your bleach. Get a spray bottle and pour the solution into it. Use it to spray down the equipment, floats, and toys. Don’t forget to wipe it down until you’re confident it’s clean.

By doing this two steps, you’re sure your swimming pool is protected from the reintroduction of mustard algae.

Brush the Pool Surfaces

The next step is to get rid of as much mustard algae from the pool before adding the killer chemicals. That calls for brushing and brushing until the surfaces get their life back.

You will need a pool brush, which you’ll have to choose according to your pool type:

  • Concrete pool: the best brush is a metal/wire pool brush
  • Fiberglass pool & Vinyl Liner Pool: here, you can use a soft vinyl pool brush with thick bristles

Since mustard or yellow algae-like clinging and sticking onto the small hidden spots in a swimming pool, don’t forget to get a brush small enough to reach into the small suspension. If there are some spots that you can’t reach with a brush, a manual vacuum is also an alternative.

When vacuuming, make sure you’re cleaning to waste to avoid bringing the algae back to the pool. The whole idea of removing the microbial has to also prevent it from coming back.

Avoid robotic or automatic cleaners. They won’t be able to catch the sneaky algae; it’ll blow right through.

Balance the Pool Chemistry (pH and Alkalinity)

It’s time to add some chemicals. That means you have to gear up. Wear yourself the necessary protection gear, including chemical-resistant gloves and goggles. A mask and apron would also come in handy, considering come chemicals might produce dust and fume.

When ready, it’s time to test the pool water. Pick up your pool water testing kit, either test strips, liquid test kit, or a digital tester. You can get them in a pool store near you or order one online.

You want to make sure the pH and Alkalinity are balanced since the next step requires adding a lot of chlorine to shock the pool for the treatment to be effective.

No matter the testing method you use, make sure these two are balanced before proceeding. If not, get a pH decreaser to decrease the pH levels or a pH increaser to increase the pH levels. Do the same with Alkalinity.

After adding the chemicals to balance the pH and Alkalinity, wait at least an hour before retesting it to ensure the levels are correct.

Triple-Shock Your Pool

Typically, pool chocking is the ideal treatment of mild green algae infestation. However, since you’re dealing with chlorine-resistant Yellow algae, a single-dose shock won’t cut it.

It would be best to triple the usual dosage to make sure you kill and get rid of the mustard algae. That means you’ll need to add 3-pounds of calcium hypochlorite pool chock to a 10,000-gallon swimming pool. If you have a 20,000-gallon swimming pool, you’ll need to add 6-pounds of the same treatment.

Pro tip: it doesn’t matter the type or brand of calcium hypochlorite shock you use. However, the higher the calcium hypochlorite percentage as the main active ingredient, the stronger and reliable the pool shock will be.

Remember not to shock your pool during the day; wait until sunset to add the treatment. Why? UV rays from the sun reduce chlorine concentration in the pool water, reducing its effectiveness. That’s something you want to avoid considering you’re trying to force out a chlorine-resistance microbial.

Remember to add the pool shock all-round to the swimming pool for easy distribution. Also, turn on the pool circulation system and allow the pump to run overnight to enable the treatment to mix and circulate to all corners thoroughly.

You can also try to brush any visible yellow algae that you might have left behind. If the water is cloudy, don’t worry. The pool shocking will help clear it out.

After triple shocking your pool, the mustard algae should be gone. But if there are some remnants left, you have to make sure the pH and Alkalinity stay balanced, and the chlorine levels stay high. Recirculate the water until all the mustard algae are gone, and the surfaces are clean.

Balance the Pool Chemistry Again

Once everything is clear, retest the water and make the necessary adjustments to the water chemistry. The pH and Alkalinity must stay balanced. What’s more, you want to keep Chlorine levels on the high end, about five parts per million (5ppm), and continue brushing the surfaces.

Do this for a couple of days, and the yellow menace will be gone for good. And if it comes back, you understand what to do.

How to Keep Mustard Algae Away

After getting rid of the mustard algae, you have to take a few measures to make sure it’s never coming back to your swimming pool again. They include:

  • Test and balance pool chemistry regularly. You want to ensure the pH, Alkalinity, and Chlorine levels stay optimal all the time.
  • Keep a functional pool maintenance schedule. Ensure you run the pool pump and filter for 8–12 hours a day the whole season. Also, keep the swimming pool clean by brushing and vacuuming it regularly.
  • Shock your pool once a week all season long. Make sure you use at least one pound shock for a 10,000-gallon swimming pool. Also, don’t forget to do the shocking dusk or at night.
  • Clean everything that enters the swimming pool with bleach. That includes ladders, pool toys, floats, diving boards, steps, solar blankets, slides, and covers. They are all susceptible to harboring the nasty mustard algae and other types of algae if you leave them damp and dirty.

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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