How to Get Rid of Persistent Algae in a Swimming Pool

Test the chemical composition of the water in your pool. Find out whether the pH and chemical levels are optimum. A pH level between 7.4 and 7.6, calcium hardness between 200 and 250 ppm and total alkalinity between 125 and 150 ppm is good to keep algae away. If the chlorine levels are below 1 ppm, add chlorine tablets to bring the levels to between 1 and 3 ppm.

Loosen the algae adhering to the pool walls by scrubbing with a hard brush. Besides removing the surface deposits, this also helps the chlorine and algaecide penetrate deeper and exert their action at the point where the algae originate in the pool wall.

Select an algal treatment chemical depending on the color of the growth. Add this algaecide directly onto the spots and leave it on overnight to kill the algae. Scrub the spots the next morning and vacuum the swimming pool. Clean the filters to remove algal spores that may be lodged there to prevent them causing a reinfection of your pool.

Check the chemical levels and shock-treat the pool with chlorine. Use chlorine tablets to achieve a concentration of 10 ppm chlorine in the pool water.

Hire a professional pool-cleaning service if the problem persists. This cleaning often includes emptying the water from the pool, performing a chlorine bath and destroying algal spores by using chlorine spray over the pool surface. In cases where even this does not help, the only way to remove the algae may be to remove and replaster the affected parts of the pool.