Mustard algae in pool.

All swimming pool owners are plagued by algae, but mustard algae in pool are the worst of all. They are extremely difficult to eradicate. It is good news that mustard algae can be eliminated permanently.

If you follow the steps in this guide, you will finally be able to get rid yourself of the dreadful mustard algae.

What are mustard algae?

In fact, mustard algae (also known as yellow algae) is another form of green algae, although its hue differs from yellowish to yellow-green to yellow-brown.

It is easy to mistake mustard algae for dirt or stains on pool walls because it has a dry, powdery surface, which is different from green algae, which is slimy and clings to pool surfaces. Often mistaken for sand, dirt, or a stain in your swimming pool, mustard algae is most common in southern climes and more uncommon in northern ones. The microbe belongs to the xanthophyte family.

Algae are also resistant to chlorine, can survive outside of the water, and can therefore be carried from place to place on pool equipment, pool toys, and even bathing suits. Clearly, algae are difficult to eradicate.

How to get rid of mustard algae

kill mustard algae

1. Disinfect pool accessories

Make sure all your pool toys and accessories are thoroughly cleaned with a clean cloth and a chlorine-based cleaner (but not straight bleach).

Wouldn’t it be easier just to use bleach? If your possessions are made of plastic or rubber, you should stick with a multipurpose cleaner that will kill mustard algae without causing damage.

You can use bleach as long as you dilute it in a one-part bleach to ten parts water solution before using it.

If your pool has a shallow end, place all of your maintenance equipment there. You may also add stuff that is too bulky or awkward to sanitize by hand but might be infected with mustard algae to the pool. It will be much easier to add pool shock to sanitize everything if all your gear is in one place.

2. Brush your pool

Due to the fact that mustard algae are chlorine resistant, you will need to scrub your pool with a heavy-duty pool brush. Ensure you have cleaned the pool thoroughly, including the gaskets around the gaskets and seals, and the pool walls under the pool steps or pool ladders.

There are special brushes for cleaning pools. They are usually made of stiff stainless steel bristles. These brushes should never be used on vinyl pools or fiberglass pools.

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3. Vacuum the pool to waste mode

Use the waste mode when vacuuming your pool. As much mustard algae as possible should be vacuumed from the pool. It is possible for mustard algae to grow in your pool’s filter, so be sure to put it in the in-mode “waste”.

Due to algae’s ability to cling to cleaners and grids in the filter, removing it from the pool becomes more difficult.

After vacuuming your pool, refill it with fresh water to replace the water that was removed.

4. Test the water balance

It is essential to balance the pool water after adding water. Check and clean the filtration system. Make sure the pH level is correct. Chemical testing kits for pools are the most accurate way to check pH and alkalinity levels in your pool.


With a pool test kit, make sure you have an alkalinity level of 120-150 parts per million and a pH level of 7.4-7.6. Algae thrive in acidic waters, so it’s very important to keep the pH level in check.


5. Clean your pool filters

In the event that pool algae grow in your pool filter media, you may need to scrub it. Be sure to backwash any sand filters or D.E. filters as directed by the manufacturer.

6. Shock your pool

The pool needs to be shocked now. Be sure to multiply everything by three in the shock that you purchase to ensure that all mustard algae has been eliminated. Every 10,000 gallons of pool water needs 3 pounds of pool shock. If you don’t know how much water is in your pool, you can use a pool volume calculator to find out. Don’t shock your pool during the daytime because sunlight can weaken the chemicals’ effects.

7. Let the water circulate!

You can circulate your swimming pool with automatic cleaning settings. A 24-hour cycle should also be run on the filter.

8. Adjust chlorine levels and brush regularly

For the next 3 to 4 days, keep brushing your pool walls to ensure that chlorine shock is doing its job of killing algae in your swimming pools. Additionally, make sure that chlorine levels remain highly effective. Continue to test and adjust it.

When you get rid of mustard algae outbreak

Once the algae have completely disappeared, return floats and toys to the pool. It is very difficult to treat mustard algae after you notice it, so get started right away.

Continuing to shock your pool may be necessary if your first shock does not work. Keep in mind that the shock will attach to anything floating in the swimming pools. Be sure to thoroughly sanitize items to prevent algae in your pool from regrowing.

Another recommendation is to disinfect swimwear. You might consider using regular or color-safe bleach, depending on your needs.

kill mustard algae

How to prevent mustard algae growth in your pool?

The best solution to combat mustard algae (including yellow algae) is to prevent mustard algae in your pool. To do this, it is important to follow just a few simple conditions. Basically, it’s just keeping your pool clean.

1. Test your water

The pH and alkalinity levels of your pool should be checked regularly with test strips. It is recommended that a pool’s pH be between 7.4 and 7.6. Alkalinity should always be between 80 and 140 parts per million (ppm).

Since algae in your pool prefer high pH waters, you’ll usually need to lower the pH to control them. Hydrochloric acid or sodium bisulfate will lower the pH level in your pool. Once you have stabilized the pH level in your pool, the alkalinity should follow.

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2. Shock your pool weekly

Using pool shock on a regular basis is the best way to ensure that unwanted organisms and harmful bacteria are killed regularly and algae blooms are prevented. You can use several products, but they usually aren’t too expensive or complicated. Use the product once a week according to the directions.

3. Keep the pool surface clean

Clean your pool water as it gets dirty. Do not allow leaves, twigs, or other debris to remain on the surface of the water for long periods of time. Also, use brushes to clean the entire pool wall and flat areas. A robot vacuum can be a great tool for regular pool maintenance.

4. Run your pump and pool filter

Mustard algae or other types of pool algae are very fond of breeding in still water. It is necessary to keep the water moving by running your pump and filter 8 hours a day, on average, in order to keep algae from growing.

What to do after treatment

In order to completely get rid of mustard algae (yellow algae) in your pool, you should take some immediate measures to ensure you’ve killed all the hard-to-see spores that may take over the pool.

  • Water chemistry levels, such as pH, alkalinity, and sanitizers, should be adjusted and balanced again and checked daily for the next week.
  • Keep your chlorine level at the optimal level.
  • Throughout the next few days, run the filter 24 hours a day. After that, make sure to run it for at least eight hours every day.
  • Pay attention to any spots where remaining algae is dressed up as sand, and brush the pool repeatedly and regularly.
  • After every brushing or robotic vacuum insert, vacuum the pool.
  • An algaecide should be applied 4-7 days after the shock.

What is Yellow Algae?

yellow algae

Green algae in the form of yellow algae or mustard algae can be resistant to chlorine and other sanitizers. Unlike green algae, yellow algae cling to the surfaces of the pool regularly, such as the walls and the bottom, as well as objects like lights and ladders, and other pool equipment.

On or around the pool, it often appears as dirt or sand-like materials. It can also be found on the equipment and water toys.

Yellow algae and its causes

Mustard algae (yellow algae) pose a significant problem. As a result, the algae spores can find their way into your pool through your pool equipment and bathing suits contaminated with the algae spores, or through weather elements, such as rain or wind.

Your location and specific situation will determine how fast the algae bloom will spread. Here are some factors that influence how fast it grows:

  • When the days are sunny and the weather is mostly warm.
  • Carbon dioxide or nitrogen levels in your pool are too high.
  • The water is not cleaned, maintained, and sanitized properly.
  • There is an imbalance in the pool’s chemical composition.
  • Circulation should be observed.

The two main reasons for yellow algae are a lack of chlorine and improper filtration. The length of runtime, the number of bathers, the speed of a pump, and the weather all contribute to these factors.

With a pump running for six hours a day during August, a swimming pool in Florida will not be clear. You should begin by running the pump for at least 8 hours a day.

You should also take into account how well the filter is functioning. Algae is more likely to appear if your system is in need of repair, broken, or clogged. Leaks also encourage mustard algae growth.

With leaks in your pool, maintaining the right level of chlorine is next to impossible. Usually, mustard algae (yellow algae) appear as winter turns to spring in most parts of the country. During summer, the warm climate, humidity, and heat create an ideal environment for algae to flourish.

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