Mustard Algae in swimming pool

Pool Maintenance: What in the Heck is Mustard Algae?

Mustard algae, commonly referred to as yellow algae, is chlorine-resistant algae that clings to the surface of the pool water and on the walls of your pool. It often starts on the shaded side of the pool and can form a sheet along the surface. Mustard algae are difficult to eradicate, as re-infection is common.



Mustard Algae  are typically brought in as spores via the rain, wind, fallen particles and debris. Algae spores can grow quite rapidly, but certain conditions can increase the time frame. Poor pool circulation from a clogged filtration system, increased sunlight and water temperatures all can lead to even more rapid growth. And its no joke when we say Mustard Algae is harder than green algae to keep away once you have had it


There are certain characteristics that are specific to mustard algae. This variety is extremely chlorine resistant, and will survive in pools with high levels of chlorine. Although it easily brushes away, mustard algae will quickly return, usually in the same spot. Unlike some  other common algae, mustard algae are not slimy and are often mistaken for iron or copper staining. Mustard algae will not create murky or hazy water, the algae forms in sheets that cling to the bottom and sides of the pool, however, the water remains otherwise clear.


How often should I use an algaecide in my pool?

Algaecide should be added to your pool water on a weekly basis. Preventing algae is the key to fun in your pool. Algaecides act as a backup to your normal sanitization program and prevent algae from starting and growing in the pool. Algaecide should be added after every shock treatment.


There are a few measures a person can take to prevent the formation of mustard algae. Use the pool on a regular basis and maintain general pool cleanliness by cleaning items used in the pool, such as toys and ladders. Regular pool maintenance, such as maintaining adequate sanitizer levels, running the filter at least 10 hours per day and weekly vacuuming and brushing of the pool surfaces and walls, is also important in mustard algae prevention. Other preventative measures include shocking the pool and adding algaecide on a weekly basis.


Once mustard algae infects a pool, begin treatment by balancing the water, ensuring the pH is correct and checking and cleaning the filter system. Utilize automatic cleaning settings to increase circulation and run the filter for 24 hours. Shock the algae with thorough brushing–use steel bristled brushes for a plaster pool and nylon brushes for a vinyl pool–add algaecide and brush the pool again. After everything settles, vacuum up the waste and filter. For ongoing mustard algae, drain the pool, utilize pressure or acid washing to kill any embedded algae roots, and change or clean the filter.

Contact Blue Fin Pool and Spa for more information! We carry an extensive line of the highest grade products for sanitizing, shocking, oxidizing, and prevention that are both user-friendly and effective. Stop in, give us a call, or send us a message!  Our team is available to answer all of your questions and make sure you have all the information you need to be confident in a pool or spa treatment plan that is the best for your situation.

Weekly Maintenance Appointments Available!

Also, Blue Fin Pool and Spa is more than happy to do the work for you! Don’t have time to keep up with the pool water chemistry? Our team offers  a weekly maintenance 3-tier program to fit every pool and budget. the ultimate pool luxury, with out the hassle.