How to Get Rid of Mustard Algae in Your Pool (4 Easy Steps)

The mustard algae in the pool (also known as golden algae or yellow algae) are rare. But what should be done if the swimming pool is infested, and how do you permanently remove the mustard algae from the pool?

Mustard algae are yellow-greenish and can be easily removed from the pool, like the green algae. In the event of an infestation of the yellow algae in the pool, the pool owner only needs a brush and a filter system. If mustard algae plague the water, a pool shock is necessary.

In this article, I explain how to remove the yellow mustard algae in the pool and what to do if it occurs again.

Kill mustard algae in 4 steps

In addition to the green algae, the mustard algae are relatively easy to remove from your pool, but certain pool equipment is still required for a successful cleaning:

  • An Agent that is used specifically against algae.
  • Chlorine granulate or liquid chlorine for shock chlorination.
  • Chlorine tablets to produce free chlorine.
  • A Pool Floater to dose the chlorine tablets.
  • Pool test strips for general water treatment.
  • A classic pool brush and a telescopic rod.
  • Safety glasses and plastic gloves.

My recommendation: Avoid advice that swears by home remedies and only use certified products for your pool maintenance.

Do you have it all together? Then you can get down to the business.

First, I will explain how you can remove a light mustard algae infestation in the pool.

This chapter is ideal if you don’t want to use chlorine unnecessarily.

Is your pool contaminated over a large area?

Then jump straight to the chapter on how to proceed if the mustard algae repeatedly appear in your pool.

Here, tough measures are carried out that promise a high guarantee of success.

Of course, you can also jump straight to this chapter to ensure that the mustard algae will be completely eliminated.

1. Brush the pool to remove the yellow algae

It is also important to brush your pool thoroughly to get rid of the mustard algae.

Use a sturdy pool brush and sponge on the difficult spots.

I recommend a steel brush for a concrete pool – not suitable for PVC pools.

To be safe, it is best to brush the entire basin and not just the visible areas.

The infestation of yellow algae (mustard algae) in your pool can be more advanced than you initially assumed.

To remove the mustard algae in your pool and to avoid repeated occurrences, I recommend brushing your pool thoroughly on the first run.

2. Run the pool pump

After all visible areas and your pool have been cleaned over a large area with the pool brush, the filter pump can be started.

However, you should first measure the water quality in your pool with a water tester.

After all, scrubbing the yellow algae and filtering is only beneficial if your pool parameters ​​are right.

  • The pH level should be between 7.2 and 7.6
  • The alkalinity has a value between 80 and 120 ppm
  • The calcium hardness is optimal at a value of 200 to 400 ppm

Then let the pump run for a few hours until the water clears again.

But we’re not done fighting the mustard algae yet – The next step is scrubbing again.

3. Scrub the pool again

If the pool is slightly soiled by mustard algae, it is not absolutely necessary to scrub the pool again.

Nevertheless, I recommend scrubbing the pool a second time over a large area while the pump is running.

Algae form cell walls, and scrubbing damages these walls. This increases the effectiveness of the disinfectants used.

This process ensures that all mustard algae in the swimming pool are removed.

In the worst case, the procedure has to be repeated, creating additional costs and wasting time.

4. Continue to control the pool water

After the water has become clear again, you should check the water quality again and, if necessary, improve it with a pH plus or a pH decreaser.

For a repeated appearance of the yellow algae in a pool, I recommend continuously producing free chlorine in the water.

A pool floater with the appropriate chlorine tablets is suitable for this purpose.

Also, make sure that the water quality is right, the pool pump runs long enough, and that the surface in the pool is brushed regularly.

You have successfully removed the mustard algae in your pool.

Tip: In the article, you will find preventive measures against mustard algae further down.

What to do if the mustard algae appear repeatedly in your pool?

Yellow algae can develop in your pool, even with proper water treatment.

It may well happen that the yellow algae were not completely removed during the first run, and that mustard algae can be found again in your pool after a short time.

Here, tough steps are required to permanently remove the golden algae from your pool.

This procedure suits everyone who wants to eliminate 100% of the yellow algae in the first run and prevent them from recurring.

1. Check the circulation time

One of the most common reasons why mustard algae cause yellow deposits in your pool is too short a circulation time for the water.

So before we continue with the tough measures, first check the running times of the pool pump. 6 to 8 hours a day is good – you can read more about the topic in the blog under the link.

The pump’s running time can easily be calculated using the following formula.

Pump running time in hours = (2 x water volume of the pool in m³) / pump flow rate in m³ / h.

Also, check whether the filter sand is clumped and may need to be replaced.

As a rule, the filter sand should be replaced every 1 to 2 years.

My tip: You can easily loosen soft lumps in the sand filter system with a suitable calcifying agent.

2. Carry out a pool shock against mustard algae on the ground

Are the yellow algae mostly only found on the pool floor?

If so, the first thing to do is turn off your pool pump.

Take some chlorine granulate with a shovel and sprinkle it over a large area on the pool floor.

I recommend you buy the following chlorine granules.

Do not aim at individual spots in your pool, and be generous with the application.

Ideally, you should wear protective goggles and a mask, as chlorine granules are easily blown in the wind and get into the eyes and respiratory tract.

After your pool has been scattered over a large area, your pool is left to rest for 24 hours so that a chlorine cushion is built up.

The pool will be brushed, and the pump switched on after the time has elapsed.

3. Shock chlorination in the case of an extensive infestation in the pool

But what should be done if the mustard algae nest not only on the ground but also on the walls?

I advise performing a pool shock with liquid chlorine in this case – you can find a suitable agent here.

Since liquid chlorine is always differently concentrated, adhere to the following quantities to avoid over-chlorination in the pool.

  • Chlorine content of 80 g / l = use 10 liters of liquid chlorine per 25 m³ of water.
  • Chlorine content of 150 g / l = 5 liters of liquid chlorine per 25 m³ of water.

When the pool pump is running, the liquid chlorine is tipped into the flow of the return nozzles.

After using the liquid chlorine, the pump must run directly for 24 to 36 hours until the chlorine content in the pool has normalized again and is below 1.5 ppm.

Then the water should be clear again – if necessary, let the pump run a little longer.

Extra tip: The use of a flocculant in your pool improves the filter performance. You can find out more in the linked article.

4. Thoroughly scrub the pool

The shock chlorination is still running, but your pool cleaning is far from over.

After the pool shock, it is important to clean your pool with a brush. Do not wait until the 24 hours are up after using the liquid chlorine.

Pick up the pool brush and scrub as hard as you can!

Scrubbing your pool 2 to 3 times should be enough against the mustard algae.

Alternatively, you can also use an electric pool robot against algae. Using a pool robot saves a lot of time and effort.

5. Use an algaecide for safety

In the meantime, I recommend using an algaecide in your pool according to the manufacturer’s specifications.

The following algae remedy against yellow algae is recommended.

To increase the effectiveness of the algaecide, I recommend adding approx 125 g of chlorine per 25 m³ of pool water, provided that this value was not already reached during the shock chlorination.

If the water foams during use, this is due to the algae agent. You can prevent this by using a non-foaming algaecide.

Preventive measures against mustard algae in the pool

Purifying water in your pool isn’t all you can do to remove mustard algae. It doesn’t even have to be necessary to remove the mustard algae.

To do this, follow these preventive measures against mustard algae:

  • Wash your swimwear: The mustard algae often get into your pool through worn swimwear in a quarry pond or lake. Therefore, you should wash your bathing suit thoroughly or swap it before taking a bath in your pool.
  • Continuous pool maintenance: Permanent pool maintenance is essential against algae – no matter their color. Therefore, let the pump run for 6 to 8 hours a day and use an algaecide.
  • Test the pool water: You must continuously test the pool water parameters. Only if you know the values ​​can suitable care products against algae be used – ideally, you use an electronic water tester for precise measurement results.
  • Disinfect the pool equipment: Mustard algae can survive outside of pool water for a certain period. After thoroughly scrubbing and vacuuming the pool, the pool equipment should be disinfected.
  • Brush the pool regularly: The floor in the pool is not only scrubbed with a pool brush when there is heavy algae infestation. Make sure that the pool is scrubbed extensively at regular intervals.

As you can see, it’s not that much work.

With appropriately good water treatment, you should simply get the problem with algae under control.

FAQ: Yellow algae in swimming pools

In this part of the post, you will find more interesting questions from readers and my answers that can be useful in the fight against mustard algae.

What do mustard algae look like?

Mustard algae belong to the yellow algae (Chrysophyta) group and can be recognized as a yellow-green coating in the pool.

It is likely mustard algae if you find yellow buildup in the pool. Source.

The mustard algae are often mistakenly mistaken for sand in the pool by beginners.

Shock chlorination must occur at the latest when large areas of yellow spots in the pool or yellow water in the pool are visible.

How are the yellow algae formed in the pool?

The mustard algae can find its way into the pool in several ways.

It is possible that the yellow algae landed in the pool water through pollen or ducks.

But humans themselves can also have brought in the yellow algae.

This usually happens when you have bathed in a piece of fresh water and go back into the pool with your unwashed clothes.

If the water treatment is still inadequate, it is a matter of time before a yellow coating forms in the pool.

I explained in detail above in the article how to remove the yellow mustard algae.

What to do if the pool shock did not help against mustard algae?

It can happen that despite shock chlorination (pool shock), the mustard algae are not removed, and the pool water remains cloudy.

A reader contacted me in this case and told me that the pump had been running for days and that the pool was cloudy even after the instructions.

After a brief exchange about the procedure, I had the strong suspicion that the water values ​​in the pool were not correct.

Test strips were used for testing. I then recommended using an electronic water tester and reporting the remaining values.

Interestingly, the pH was 7.27, and the total alkalinity (acid capacity) was 81 ppm and thus still in the green area – the free chlorine was also abundant in the pool.

But the cyanuric acid was too high at 106 ppm and well above the ideal range of 30 to 50 ppm – that was the problem if the pool remained green despite pool shock.

In my specialist article on cyanuric acid, I mentioned that the effect of chlorine continues to decrease if there is too much chlorine stabilizer in the water.

A partial water change had to be made in the pool to lower the cyanuric acid – how much exactly I explain in the blog article under the link.

Then the pool was cleaned again against mustard algae using the instructions.

You see, precise measurement results brought the decisive success that saved further costs and nerves in the water treatment.

Do you have any further questions about the yellow algae in the pool?

Just write me a message on my social channels on Facebook, Twitter, and Pinterest under @contactswimfool.

Happy swimming!

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Hi. I'm Max Berg. I've been in the pool industry since 2015 and have always felt drawn to water. I'm the author behind swimfool.com, where I share my years of experience in pool maintenance and give helpful tips on keeping a swimming pool or hot tub clean. My tips reduce the costs of water treatment and protect the environment.

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