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How Do I Treat Mustard Algae In My Swimming Pool?

How Do I Control Mustard Algae in My Swimming Pool?

Mustard algae, also known as yellow algae, is a common problem for pool operators, primarily in the southern region of the United States. Unlike green algae, mustard algae appear as yellow or brownish spots and cling to pool walls, floors, and swimming equipment, making it difficult to remove. Understanding how to identify, prevent, and control mustard algae can help maintain a clean and safe swimming environment. In this article we're going to explore a comprehensive approach to managing mustard algae in your pool.


What is Mustard Algae?

In order to fight it, we first need to know what mustard algae actually is. Mustard algae is a chlorine-resistant form of algae that thrives in warm, sunny climates. It often looks like pollen, dirt, or sand but doesn't brush off easily. If left untreated, it can spread quickly and become a recurring issue.

How Do I Know If I Have Mustard Algae?

Mustard algae are typically found:

  • In warm, humid locations 
  • Pools close to open space, forests, or swampy areas
  • areas with a lot of wildlife that enters the pool or pool area

In the pool itself, mustard algae typically is found:

  • In shady areas of the pool.
  • On the walls and floors of the pool.
  • On pool equipment and toys.
  • In areas with poor circulation.

It appears as yellow or brown spots that can be easily mistaken for dirt or sand. Unlike other types of algae, mustard algae don't float freely in the water but cling stubbornly to surfaces.


Preventing Mustard Algae

Prevention is the best approach to dealing with mustard algae over trying to eliminate it once it appears. Let's explore some easy steps in preventing mustard algae from appearing in the first place:

  1. Maintain Proper Pool Chemistry: Regularly test and balance your pool water. Ensure that the pH, alkalinity, and chlorine levels are within the recommended ranges. We recommend you keep your free available chlorine levels at 4 p.p.m. for best results. 

  2. Regular Cleaning: Brush and vacuum your pool at least once a week. Pay special attention to areas with poor circulation, such as corners and steps.

  3. Disinfect Pool Equipment & Toys: Contaminated pool equipment and toys brought in from the outside world can cause mustard algae to be introduced to the water. Be sure to thoroughly rinse all equipment and toys, followed by a disinfection spray down if possible before allowing said items to enter your pool. 

  4. Clean Suits & Shower Before Swimming: Encourage swimmers to wash their swimming attire and shower before entering the pool to remove any contaminants that might introduce algae spores.


Treating Mustard Algae

We can do everything within our power to prevent mustard algae from entering our pools, but sometimes it just sneaks in! If you do happen to find mustard algae in your pool, it's essential to act quickly in order to prevent it from spreading. Here's how to treat it effectively:

  1. Brush and Vacuum to Waste: Thoroughly brush all surfaces where mustard algae are present. Use a pool vacuum and set your filtration valve to waste to remove the algae from the pool.

  2. Hyperchlorinate The Pool: Use a pool shock treatment to kill the algae. For mustard algae, you may need to use a higher dose than usual. Follow the instructions on the shock treatment product for best results.

  3. Apply Algaecide: After shocking the pool, add a mustard algaecide to help kill any remaining spores. Again, follow the manufacturer's instructions for the correct dosage.

  4. Clean Pool Equipment: Remove and clean all pool equipment, toys, and accessories that have been in the water. Soak them in a solution of chlorine and water to kill any remaining algae spores.

  5. Monitor and Adjust: Keep a close eye on your pool's water chemistry and make any necessary adjustments. Test the water daily until you are confident the algae are gone.


Long-Term Algae Control

After treating mustard algae, take steps to prevent it from returning:

  • Chlorination: Seek to maintain a free available chlorine residual of 4 p.p.m. at all times in the pool.
  • Consistent Maintenance: Maintain a regular cleaning and maintenance schedule.
  • Monitor Circulation: Ensure your pool pump and filter are functioning correctly and providing adequate circulation.


Controlling mustard algae in a swimming pool requires diligence and regular maintenance. It also requires a lot of know-how to keep a swimming pool running in general, which is why we offer our award-winning Certified Pool Operator (CPO) Certification! This program walks you through all the in's and out's of swimming pool and hot tub operation so you don't have to stress or worry about if what you're doing is the right or wrong way to approach taking care of an aquatic facility. 

Pool Training Academy's fully accredited CPO class is a great way to learn everything you need to become the best aquatics operator you can be. Our fully online class offers you the flexibility you need and our in-person courses offer that classic classroom feel. For more details or to get signed up click here


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