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.

What is Mustard Algae
Mustard algae, commonly referred to as yellow algae, is chlorine-resistant algae found in sunbelt areas such as California, Texas and Florida. This alga is a wall-clinging variety that resembles sand or dirt and grows in the bottom or sides of the shady parts of a pool. Mustard algae are difficult to eradicate, as re-infection is common.

There are a few different factors that cause mustard algae. Algae spores enter pools in various ways, including contaminated equipment or swimsuits, rain, and wind. Under certain conditions, algae will quickly bloom, seemingly overnight. These conditions include warm temperatures, the presence of carbon dioxide or nitrates, out-of-balance water and warm sunny days. Poor pool care, including a lack of circulation, poor sanitation, and filtration, is also a cause of mustard algae.

There are certain characteristics that are specific to mustard algae. Mustard algae create a high chlorine demand but are 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 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.

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 infect 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.

Here Are Some Products We Recommend


Concentrated Algae Kill
Fast-acting, triple chelated, 7.41% copper algaecide designed to control mustard algae.

Fast-Acting, Long-Lasting Treatment to Control Algae Growth
Will not cause water to foam
Will not alter the pH or chlorine content of the water

Yellow Out®
Amazing Yellow Algae Cleanup Results

Yellow Out is a chemical breakthrough! Amazing cleanup results when used prior to shock treatment with an EPA-Registered chlorinating compound that kills green or mustard algae.