Mustard Algae In Pool: What It is, How to Remove & Prevent

Mustard Algae In Pool

A clean pool is every pool owner’s dream. However, mustard algae may infest your pool, making the water cloudy, hazy, and unhygienic to swim in.

This article will help you to conceptualize what mustard algae are, how to get rid of them, and the steps you should take after treating your pool. It will also provide important pointers on how to prevent their infestation in your pool.

What is Mustard Algae? 

Mustard algae is a form of green algae that grow in clusters on your pool surfaces and floor. They appear as yellow spots that are easily mistaken for dirt, pollen, or pool stain.

Unlike green algae, they are powdery, non-slimy and they make the water look cloudy or hazy. They are classified as xanthophytes and are resistant to normal pool chlorine levels because they contain compounds that resist the oxidation efforts of pool sanitizers.

When brushed, they come off with ease but are quick to reinfest the same surfaces. Therefore, they can be easily reintroduced to your pool through infected pool accessories that have been used in natural water bodies such as lakes.

How to Remove Mustard Algae 

How to Remove Mustard Algae


1. Decontaminate the Pool 

Decontaminating pool accessories such as bathing suits, floats, toys, and any other pool equipment will go a long way in keeping these algae at bay.

This decontamination involves a thorough cleaning of the accessories because they are the main culprits in the introduction of mustard algae in a pool. For this, use a chlorine-based cleaner and algaecides that target mustard algae.

Be sure to follow the instructions on the algaecide’s packaging label for the best results. Further, in the case of bathing suits, bleaching them in the washing machine will effectively decontaminate them.

You should also clean and decontaminate your pool filter because once the mustard algae infest your pool, they accumulate on the filter too. Ideally, you should brush your pool surfaces and floor to loosen the mustard algae in readiness for the next step; pool vacuuming.

2. Vacuum the Pool to Waste

This is an important step because it aids in the removal of the mustard algae and other debris from the pool floor. This step requires you to connect your vacuum to the waste line/valve.

During vacuuming, ensure the water level is above six inches. If it drops below that, refill your pool for effective vacuuming. Repeat this process until you get rid of all the mustard algae in your pool.

Read More: How to Vacuum a Pool

3. Using Pool Shock

Pool shocking is important because it kills the mustard algae that may be left in your pool after vacuuming it. The concentrated levels of chlorine are necessary because these algae are resistant to normal levels of chlorine in your pool.

Be sure to wear protective gear while handling pool shock to avoid harming your skin. You should also avoid using the pool immediately after shocking for the same reason. Therefore, allow at least 8 hours before using your pool.

Although different shocks have unique instructions, the recommended amount for mustard algae eradication is about 3lbs. per 10,000 gallons of water. This is three times the normal pool chlorine levels.

Always read the instructions on the package for correct usage. For maximum effectiveness, apply pool shock in the evening or on a cloudy day because the sun’s UV rays break down free chlorine.

For better results, pour the pool shock near the pool jets and run the pool pump for at least 24 hours to aid in its circulation in the water. Pool shocking should be done weekly or whenever necessary.

Read More: ​When to Shock your Pool

What to Do after Treatment 

  • Test your pool water using a pool test kit and ensure that the pH and alkalinity levels are balanced. The Centre for Disease Control (CDC) recommends that pools should have a pH level of between 7.2 to 7.8.
  • Run the filter for at least 18 hours daily after the initial shocking to remove any cloudiness that may have been left behind by the mustard algae after pool shocking.
  • Using a pool water clarifier may also help to clear the water of mustard algae faster.
  • Brush your pool daily and vacuum to waste at least once after treatment to get rid of the dead algae.  

How to Prevent Mustard Algae 

How to Prevent Mustard Algae


1. Keep your Pool Water Balanced 

You can do this by regular testing to ensure that the pH is maintained between 7.2 and 7.8. Also, maintain the pool alkalinity is at optimal levels (80-120 ppm.).

If the pH is below 7.0, add alkaline to make the pool water basic. If the pH is above 7.8, add an acid to balance it out.

Read More: The Best pH Meter

2. Keep your Pool Clean

Regular brushing of your pool to loosen any algae from the surfaces is essential. Vacuuming after brushing will ensure that any mustard algae is removed before it multiplies. This keeps the pool hygienic.

3. Keep Your Water Circulating

To keep the water in your pool circulating, run your pool pump, and filter for at least 12 hours daily. Mustard algae thrive in still water. In circulating water, their chance of accumulation is lower. They will be filtered out before they attach.

4. Shock Your Pool Weekly

Weekly pool shocking is recommended because it ensures that any algae are killed before they multiply. Use 1 lb. of shock per 10,000 gallons. Always take the necessary precautions during this process and follow all the guidelines on the package.

5. Practice Good Sanitation Habits

To reduce the chance of mustard algae infestation, clean the pool and all the pool accessories every time before they are used in the pool.

You should also ensure that all pool users have rinsed themselves before swimming in your pool, especially if they have been swimming in a natural water body.


In conclusion, mustard algae infestation in your pool can be prevented by maintaining high levels of pool hygiene through proper sanitization of pool accessories.

To remove them from the pool, sanitize all pool accessories, brush your pool and run the pool vacuum on waste. Finally, shock the pool and run the pool pump for at least 24 hours to get rid of the mustard algae.