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How to Get Rid of Green Algae in a Swimming Pool

Mustard algae might sound like something you put on a hot dog, but it is actually a common type of algae found in swimming pools. It is sometimes called yellow algae because of its yellow color. If you don’t maintain the cleanliness of your pool, then don’t be surprised if you start seeing this algae form.

Although mustard algae are rather rare, it can still show up in certain circumstances. Fortunately, it is easy to eliminate mustard algae and keep it away by following a couple of simple steps.

Overview of Mustard Algae

You probably already know about slimy green algae and how it sticks to pool walls and forms flat blobs in the water. Mustard algae are a little different, though. People tend to confuse mustard algae with pool stains, sand or dirt. The algae belong to the “xanthophytes” family of microbes. They’re resistant to chlorine, so you can’t get rid of them with standard sanitizing chemicals.

Mustard algae will stick onto any surfaces or items in your pool, such as the walls. But it can’t live anywhere else but in your pool. You’ll find the algae on your pool toys, equipment, floats, and sometimes on the bathing suits of the swimmers. If you notice any mustard algae around, apply disinfectant to the algae prone areas right away.

The 5 Steps for Killing Mustard Algae

Don’t let mustard algae keep you down and depressed. Here are ten easy steps to kill mustard algae in order to keep your pool sanitized.

Clean the Filter

The purpose of a pool cartridge filter is to clean your pool water by capturing debris and decontaminates.

Shock Treatment

One pool shock treatment won’t be enough to get rid of mustard algae in the water. Therefore, it is recommended that you use 3 lbs. of shock to clean 10,000 gallons of water. Do it when the sun goes down. Turn on your pump and filtration system. Leave them on for the next 24 hours. The algae should be gone by then.

Vacuuming and Brushing Run FilterFor 24 Hours

Before you start sanitizing your pool water again, it helps to get rid of the existing mustard algae first. You can do this with a high-quality algae brush which is designed to loosen all the algae, so they’re not so clingy. Once you do this, you can easily suck up the algae with a manual vacuum. Since mustard algae may inhabit your filtration system, turn the filter’s setting on “waste” instead of “backwash” prior to turning on the vacuum.

After you’ve vacuumed the algae out of the pool, put the garden hose in your pool and add more freshwater to it. The vacuum sucked up water before, so you’re just replenishing what was lost.

Brush and Balance Again Next Day

Brush your pool walls again to ensure that no mustard algae is clinging to them. Test your chlorine levels and add more if needed. Also, test your level of alkalinity and pH regularly and make the proper adjustments to them too.

Test the Water to Make Sure There is No Algae

Do one more water chemistry test to ensure there are no algae. If the reading shows the water is balanced and everything looks clear in the water, then your mustard algae problem has been resolved.

Any pool equipment or accessories that you put in the pool during this process can be removed.


Now the only thing left to worry about is preventing the mustard algae from returning again. If you keep your water chemistry balanced, then everything should be fine. This means balancing the sanitizer, pH, and alkalinity levels regularly.

Leave the filtration system and pump running for between 8 and 12 hours per day throughout the entire season. Brush and vacuum your pool if you notice any signs of algae.

Shock treatments should be made once per week. Use 1 lb. of shock per 10,000 gallons of water. Clean all the pool items, equipment, and accessories, such as solar blankets, slides, diving boards, steps, ladders, floats, and toys. Use the cleaning solution with chlorine in it to do this. This will ensure the algae is killed.

The only mustard you need to worry about now is the kind that goes on your hot dogs and hamburgers. All other mustard, especially in your pool, has got to go.