Here’s How To Get Rid Of Mustard Algae In Your Pool (FAST)


Today I’m going to show you how you can get rid of mustard algae in your pool FAST.

By following the steps in this guide, you will get rid of the dreaded mustard algae once and for all …

And hopefully never see it return ever again.

You’ll also learn what you should be doing after treating your swimming pool for mustard algae to make sure you’ve actually killed it.

Let’s dive in!

What is mustard algae & why is it bad for your pool?

Mustard algae (also know as yellow algae) is actually another form of green algae, but it varies slightly in color: it can be yellowish, yellow-green or yellow-brown.

The problem with this pesky little nuisance is that it looks so much like dirt, pollen or sand, that often, people don’t even realize they have it.

It’s also not slimy like other algae, so it even has a texture close to that of dirt. But, why is it bad?

Well, algae itself is not dangerous to humans, but an overgrowth of it can harbor harmful bacteria that is dangerous, such as E coli. 

Also, like any other algae, it can stain your swimming pool and cloud the water, which also sticking to things like pool equipment, pool walls, bathing suits, floats and toys. Nobody wants to swim in that mess!

This type of algae usually requires chlorine plus an extra chemical like Yellow Out to finally get rid of it.

Read: The Ultimate Guide to Getting Rid of Pool Algae

Mustard algae is most commonly found in freshwater or warm water climates, but that doesn’t mean you shouldn’t keep a look-out for it anywhere you live.

How to prevent mustard algae from growing in your pool

Although mustard algae is more closely kin to green algae, it is just as hard to get rid of as black algae.

I know… I tried to keep from saying the “b” word. But it’s true, and if you let mustard algae get out of control, you might find yourself having to drain and acid wash your pool.

And nobody wants that!

The best way to get rid of algae is to never get it in the first place!

How do you do that? I’m glad you asked!

There are several things you need to be doing on a regular basis to keep mustard algae at bay.

1. Test your water

You want to test your pool water regularly with some test strips to make sure your pH and alkalinity are in proper ranges

The perfect pH level for a pool is 7.5, but ideal is considered anywhere between 7.4 and 7.6. Alkalinity should always be between 80 and 140 ppm.

Algae thrives in water with high pH levels so you will usually be lowering that level to keep it under control.

Read: How to Lower the Alkalinity in Your Pool

To lower your pool’s pH level, you will add muriatic acid, or sodium bi-sulphate. 

The alkalinity in your pool is directly related to the pH level, so once the pH level is stabilized, the alkalinity should follow.

2. Shock your pool weekly

In The Swim Pool Shock – 68% Cal-Hypo Granular Sanitizer for Crystal Clear Water – Defends Against Bacteria, Algae, and Microorganisms- 24 X 1 Pound
  • Powerful chlorine shock treatment that is great for regular maintenance.
  • Quickly eliminates algae, bacteria, and other harmful contaminants from your pool water.

Shocking your pool with pool shock is basically super-chlorinating your pool.

It’s the best way to ensure that you are killing off unwanted organisms regularly and preventing algae from blooming.

There are several products you can use, but they are usually not super expensive or difficult to use.

Just follow the manufacturer’s instructions and use it once a week.

3. Keep the pool surface clean

There are some different types of automatic pool cleaners but the robotic pool cleaner is pretty much like a Roomba for your pool (a.k.a. the best invention since sliced bread).

The great thing about a robotic pool cleaner is that it will scrub the surface and the tile lines, keeping your pool brushed and free from debris.

It’s the best cleaner for mustard algae blooms because it does the best job at picking up fine, silty debris.

If you have trouble with this type of algae, this is definitely something I recommend using. 

4. Run your pump & filter

Algae loves still, stagnant water, so you need to keep it moving by running your pump and filter an average of 8 hours a day to keep it circulating.

How to get rid of mustard algae

You might be saying to yourself, “This is all great advice, pal, but what am I supposed to do if I already have mustard algae?”

So, let’s talk about how to kill mustard algae!

As I said earlier, mustard algae is one of the harder ones to get rid of because of its stubborn chlorine-resistant nature.

How much work you have to put in will depend largely on how much algae has invaded your pool.

But a little hard work never hurt anyone, right?

Let’s get started with these 6 easy steps to banish the yellowish brownish greenish monster from your pool:

1. Disinfect pool accessories

You should wash all swimsuits that will re-enter the pool and dry on a hot setting.

Also, rinse all your pool accessories and wipe them down with a chlorine-based solution.

This is an important step because those little spores will cling onto pool toys and swimsuits and keep depositing themselves in your water.

2. Brush your pool

Blue Devil Pool Wall Brush Deluxe with Poly Bristles - 18"
  • STRONG: Metal backing provides enough strength to thoroughly clean pool walls
  • FLEXIBLE: Designed with poly bristles to help reach the toughest corners

Mustard algae will require some heavy duty scrubbing since it’s chlorine resistant, so definitely have your pool brush ready.

You will want to make sure you have scrubbed the entire pool surface thoroughly, including under steps and around gaskets and seals.

3. Vacuum the pool to waste

Vacuuming your pool to waste just means that you are diverting the water to the waste line so it can bypass the filters and cartridges. 

This is important because algae will cling to pool filter cleaners and grids, making it harder to remove it from the pool. Pool Center offers a great tutorial on that process here.

4. Test the pH balance

The best way to test the pH balance is with a chemical testing kit for your pool, which will offer the most accurate results. 

For this process, you will want your pool’s pH level to be lower than 7.6.

Use the chemicals described earlier to reduce or raise those levels.

5. Clean your filters

Your filter media may require scrubbing if you notice algae has started to populate here.

If you have a sand filter or D.E. filter, make sure you backwash these filters as directed by your manufacturer.

6. Shock your pool

DryTec 1-1901-24 Calcium Hypochlorite Pool Shock, 1-Pound, 24-Pack
  • One bag of this product per 10,000 gallons of water
  • Adjust and maintain pH at 7.2-7.6

You may have to use pool shock treatment more than once in this process, depending on how well you are able to get rid of it initially.

At this point, you can also throw your pool accessories into the shallow end to further disinfect them and kill algae spores.

What to do after treatment

Now that you’ve hopefully effectively banished the mustard algae from your pool, you will need to take some immediate precautions to make sure you’ve actually killed all those hard-to-see spores that can take bloom before you know it.

  • Adjust and balance water chemistry like pH, alkalinity, and sanitizer levels again and check them daily for the next week.
  • Adjust your chlorine levels to keep them in optimal range.
  • Run your pool filter 24 hours a day for the next few days. Then make sure you are running it at least 8 hours a day afterwards.
  • Brush the pool repeatedly and regularly, paying close attention to any spots that might be algae disguised as sand.
  • Vacuum the pool every time you brush or insert a robotic vacuum.
  • Use an algaecide 4-7 days after you shock your pool.

Bottom line

Algae is a nuisance and mustard algae is one of the most difficult to get rid of because of its chlorine-resistant nature.

I always recommend any pool-owner stay on top of their pool maintenance activities to keep problems from cropping up and getting out of hand.

But in warm-weather climates, it’s especially important because of the persistence of black and mustard algae in those areas.

Is algae plaguing your pool? Let us know if we can answer any questions. We’re happy to help!

2 thoughts on “Here’s How To Get Rid Of Mustard Algae In Your Pool (FAST)”

  1. We live in Arizona and have a pebble tech interior wall of our inground pool where this color algae has formed would we still follow the same above instructions or would it be different for that type it’s not plaster

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