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What is the Fastest Way to Clean a Swimming Pool with Severe Algae?

By Diane Watkins
Algae in the water makes it appear green.

Algae infestations can be difficult to deal with, but with proper pool chemistry and persistence the war against algae is winnable. The green slimy plant grows in pools and other water that is not sanitized regularly. Algae itself is not harmful, but it is an indication that the pool water is out of balance and needs cleaning and sanitizing. The pool should not be used until it is cleaned and the water chemistry is balanced.

The Importance of pH

Good pool chemistry is the first step in eliminating and preventing algae. Before adding the chlorine, it is important to adjust the pH levels to between 7.2 and 7.6. The chlorine is much more effective at this pH. Outside of this optimal pH range, it will take much more chlorine to have the same cleaning effect.

The Best Solution: Chlorine

Chlorine effectively kills algae at levels of 2 to 3 parts per million (ppm) or greater. Adjust the pH, then scrub the sides of the pool and add a chlorine-based shock treatment to raise the free chlorine level to approximately 3 ppm or higher. Keep the chlorine level elevated until all the algae has been killed. Turn on the pump and circulate the water for the entire time. When the algae dies and turns white or gray, it can be vacuumed and filtered from the pool. If the algae doesn’t die within 12 to 24 hours, add more chlorine shock treatment.


While commercial algaecide products seem to be the answer, in reality they do not kill algae. They are preventatives that are good at preventing algae infestation, but once the algae takes hold, they are ineffective. Use algaecides once the initial infection has been killed to prevent re-growth.

Draining the Pool

In extreme cases it might be tempting to drain the pool for cleaning. This is effective for above-ground pools, but it can be a terrible mistake for in-ground pools. It is dangerous to remove more than 1/3 of the water at a time, especially in areas with high water tables. If you feel that you must drain the pool, call a professional for advice.


About the Author


Diane Watkins has been writing since 1984, with experience in newspaper, newsletter and Web content. She writes two electronic newsletters and has a Bachelor of Science degree in chemistry from Clemson University. She has taken graduate courses in biochemistry and education.