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Algae grow in pools with imbalanced water chemistry. Yellow algae grow in pools with cool, shaded areas whenever the water’s pH levels are too alkaline. 

Balance your pool water and add 2-3 doses of a shock to kill all the algae spores. Mustard algae are particularly persistent and resist chlorine better than other algae growths. 

If you’re struggling to kill this annoying alga, continue reading to learn how to eliminate it for good! 

How Can You Kill Mustard Algae in Your Swimming Pool? 

A mustard algae outbreak can be incredibly stubborn in a swimming pool. It’s especially prevalent on swimming pool floors and walls, growing in dark corners, shaded areas, and the filter.

These step-by-step instructions are the best ways to remove mustard algae growing in your swimming pool:

  1. Test your pool water pH levels
  2. Do not adjust the water chemistry until after scrubbing your pool walls and floor
  3. Scrub your walls with a pool brush
  4. Ensure you get rid of mustard algae growing in the crevices and dark corners
  5. Use a pool net to skim out as much of the large particles as possible
  6. Bleach your clothing
  7. Sanitize your pool toys and equipment
  8. Place your pool tools in the water to sanitize
  9. Add shock treatment
  10. Continue checking your pool’s pH and alkalinity levels
  11. Shock your pool again as needed

Mustard algae spores are usually transmitted into the pool by contaminated cleaning equipment, organic material that falls in the water, and dirty clothes. To get rid of mustard algae, you’ll have to scrub all of your walls and the floor and sanitize the water.

You’ll have to eliminate all the spores and other potential contaminants. Killing the algae is the only way to completely remove all possible contaminants that can encourage more algae to grow in the pool.

Scrubbing the algae clinging to the liner in your pool and adding shock treatment is the only way to kill this alga completely. Unless you kill all the algae spores and make the pool chemistry unfavorable to organic growth, you may continue to experience a mustard algae outbreak.

What’s the Best Way to Get Mustard Algae Off of Your Pool Walls? 

Bristle brushes are among the best tools to remove algae from your pool. It would be best to use different brushes based on how badly the algae clings to your walls.

Soft brushes are suitable for exfoliating the spores from your walls, but a stiffer brush is better for breaking up hard buildup. Most softer brushes are made from polypropylene, which is suitable for everyday use.

However, try a nylon brush if you have a particularly stubborn mustard algae stain. To get rid of mustard algae growing in the corners of your swimming pool, use a smaller brush head to fit into these small corners.

Once you finish scrubbing the walls, skim the pool’s surface with a pool net, and shock your pool. Cleaning your walls and floor is essential since mustard algae can survive the chlorine shock and recontaminate the pool.

What is the Best Chemical to Kill Mustard Algae Growth? 

Shocking, also known as super chlorination, is the best chemical treatment to get rid of mustard algae. However, you should triple-shock your pool rather than add a single dose of chemicals to your water.

A triple shock treatment of your pool will corrode and break down the molecular bond of mustard algae. Algae are relatively chlorine resistant, making it difficult for normal chlorine levels to permanently kill off the spores.

If you clean contaminated clothes, use bleach or color-safe bleach to kill the spores. However, don’t use bleach on your pool toys and pool equipment. The bleach might be too harsh and harm the plastics.

Use a chlorine-based cleaner or diluted bleach on plastic or rubber equipment.

How Long Does it Take to Kill Mustard Algae Growth? 

There’s not really a standard time it takes to kill mustard algae. The time frame can vary depending on how well you scrub your walls and floor and sanitize your pool equipment.

As a rule of thumb, mustard algae is usually killed within 48-72 hours after your shock your pool. However, whether your pool is entirely algae-free depends on whether any spores survive.

You’ll have to continue scrubbing your pool floor and walls until the algae in your pool are gone. If you don’t remove and kill all the spores, they will most assuredly come back as soon as the pool pH permits.

Ensure you shock your pool with a heavy dose of chlorine once you finish scrubbing your pool. This should hopefully kill off the spores after they’ve been loosened from the pool liner.

Should You Sanitize All of Your Pool Equipment in the Swimming Pool? 

Some people place their equipment in their swimming pool so the chlorine cleans all the mustard algae spores from the tools. This is an especially efficient and effective way to ensure everything is clear of spores and won’t recontaminate your pool water after clearing away the algae.

It’s an especially effective method if you have a shallow end to your in-ground pool. You wouldn’t want to put your tools in the deep end because it’d be tough to get them back out again.

If you don’t have space in your swimming pool to sanitize your equipment, you should soak them in another container. Soaking your tools in a chlorine solution gives the best results and prevents mustard algae from re-growing.

Alternatively, you could wipe your tools down with bleach or chlorine spray to remove the spores. This will take significantly longer and is less effective than soaking your equipment. But if you clean your tools two to three times, you should get the desired results.

How Can You Prevent Mustard Algae Growth in a Pool? 

Keeping your pool water chemistry balanced is the most crucial step to preventing algae in your pool. If your water is too alkaline and the pH above 7.6, it could become a breeding ground for bacteria, fungal spores, and algae.

Maintaining a balanced pH will prevent mustard algae from growing since the pool sanitizer levels will be at optimal levels. Whenever your pool pH levels are too high or low, it disrupts how your chlorine works and keeps the water quality healthy.

Regularly use your pool brush and net to remove excess debris and spores from your pool water. This will help prevent algae in your pool by removing calcium buildup and other mineral deposits that can offset your pool’s balance.

Test your pool water every day or two to ensure the pH level is right. Scrub your pool wall and floor to clean any algae, mold, and calcium at least once a week. Finally, clean more obscure places at least once or twice a month, like pool ladders, pool covers, and diving boards.


Mustard algae can be a very annoying polluter of your swimming pool water quality. Mustard algae are difficult to kill, and if left untreated on your pool wall and floor, they can leave stains. Attacking this growth fast is best to prevent any damage or stains to your pool and equipment.

It’s best to prevent algae in your pool, but if you see it developing in the corners, test your water and shock immediately. Protect your pool liner and tiles from this bothersome contaminant.

If you want to learn more about the different types of algae in a pool, check out our article on how to get rid of black algae in a pool!


What Exactly is Mustard Algae? 

Mustard algae is a highly resilient form of algae that typically grows on pool walls and floors. These algae developed highly protective cells that resist compounds like chlorine. Killing this alga is difficult because as long as small particles survive a chlorine treatment, they can respawn and take over the pool once again.

Is Mustard Algae the Same as Yellow Algae? 

Yes, yellow algae is another common name for mustard algae. Most pool experts interchange these terms since yellow algae is a common nickname. In some instances, the term “yellow algae” is used because it’s more generic and easily understood.

How Does Mustard Algae Differ From Green Algae?

Green algae are less resistant to bleach and chlorine than their yellow counterpart. It also usually grows in warm, sunny areas of the pool, whereas yellow algae prefer shady, cool water. 

Should You Use Bleach in Your Pool to Kill Algae?

You can use bleach in your pool to kill algae spores, but it shouldn’t be used the same way you use chlorine and bromine. Bleach works better as a sanitizer for surfaces since adding it to your water can throw off your pool chemistry. Use bleach to clean plastic and tile surfaces, like pool walls and ladders.