How To Get Rid Of Mustard Algae

Here's a very simple guide that will walk you through how to remove stubborn mustard algae from your swimming pool.

Mustard or yellow algae is a rare form of pool algae that is more common in warmer areas, but that doesn’t mean your pool won’t be infected. It’s important, that if you spot signs of mustard algae, to act quickly and get rid of it.

What is Mustard Algae?

Mustard algae is rare and often mistaken for sand, dirt, or a stain in your pool. It’s not slimy like regular green algae, but it likes to attach itself to pool walls and other items.

It’s also chlorine-resistant and very stubborn. It can even live outside of your swimming pool. That means pool equipment, toys, floats, and even bathing suits. If you have mustard algae, you’ll want to disinfect these items right away.

Are you sure it's Mustard Algae? Check out our green pool water guide and algae guide to see if what you have is really mustard algae.

How to Kill Mustard Algae is 10 Easy Steps

Here is a simple step-by-step guide to getting rid of the algae. Most of these steps are also there for prevention of mustard algae because you know what they say, an ounce of prevention is better than a pound of cure!

Machine Wash Your Swimmers

Wash all of your bathing suits in the washing machine and dry in a dryer. This should kill the algae if it has infected these items.

Clean Your Toys and Floats

Disinfect all toys and floats with a chlorine based solution. Clorox cleaner (not bleach) should work just fine in this case. You don’t want to bleach your toys and floats.

Move Equipment to Shallow End

Place all maintenance equipment, including hoses and poles, in your pool (the shallow end, if you have one). When you treat the pool with shock, this will sanitise all your equipment. You can also throw anything you think might be infected with mustard algae in the pool.

Vacuum The Algae OUT

Fill up your pool with fresh water to the very top. Hook up your manual vacuum cleaner (do not use an automatic vacuum for this) and turn your filter to waste, not backwash.  

Get Your Water Tested

Make sure your pool water is properly balanced using a test kit. Your pH levels should be between 7.4 and 7.6 and your alkalinity should be between 120 and 150 ppm (parts per million). This will allow the shock treatment to be more effective.

Brush your pool

Brush the algae off your pool walls and floor using a pool brush. Also, brush the entire pool. You want to break up the algae and get it in suspension so that the chlorine from the shock can attack and destroy it.

Triple Shock Your Pool

Just like a regular algae-killing treatment, you want to shock the heck out of it! 1.5kg per 40,000L of water. Make sure you shock at dusk or night time, and leave your filter and pump running 24 hours a day until the algae is gone.

Keep Brushing

Keep brushing your pool for the next couple of days. It’s a good idea to keep your pool properly sanitized during this time.

Keep checking your pH and alkalinity levels to make sure they stay in range. You want to keep that algae from attaching itself to anything, like the walls and floor of your pool. If the algae is in suspension, you will have an easier time killing it.

Make Sure It’s Safe

After a couple of days, if the algae seems to be gone, it’s safe to take any toys, floats, equipment, and bathing suits out of the pool.

I would suggest shocking your pool one more time for good measure. It doesn’t have to be a triple shock, you can just use one pound of shock per 10,000 gallons. Just make sure your filter is still running and you shock at night or dusk.

Check and Repeat

After you’ve done your final shock treatment, it’s time to test your water and repeat if needed.

If the water chemistry is good and the water looks clear, then you should be fine for now. If, however, the pool water isn’t chemically correct, be sure to get it back where it needs to be.

How to Prevent Yellow of Mustard Algae from Growing

Keeping your pool properly balanced and sanitized is the key to keeping all forms of algae from growing. Make sure you:

  • Keep your pH, alkalinity and sanitizer levels in the correct range at all times.
  • Run your pump and filter for 8 to 12 hours a day all season long.
  • Keep your pool clean by regularly vacuuming and brushing.
  • Shock your pool every week. One pound per 10,000 gallons.
  • Keep your additional pool equipment clean including pool toys, floats, ladders, steps, diving boards, slides, solar blankets and covers.

Easy way to get rid and prevent Mustard Algae

One of the best ways to get rid of mustard algae is to prevent it altogether! Although your traditional algaecide works well on regular green algae, mustard algae is a different beast in itself. If your pool suffers from mustard algae and you don't want to go through the trouble of dealing with them ever again, we HIGHLY recommend using an extra-strong algaecide like Water TechniX Algaecide. This is specially formulated to deal with not only regular pool algae, but for extremely tough and annoying strains like mustard algae!


Keeping your pool free from Mustard Algae isn't only good for the eyes, but it is healthy as well. Unchecked, mustard algae can overrun your pool and infect everything, causing damage to pool surfaces and can even cause health issues to those who are sensitive to it. While it may sound like overkill, follow the steps we have outlined above at the very first sign of mustard algae. You'll not only have an easier time at it, but you're going to prevent an even bigger outbreak down the line.

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Happy swimming :)

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