Shock your swimming pool with high levels of chlorine. Find the recommended dose of chlorine for your size swimming pool. Add ten times the normal amount of chlorine to the water. Pour all of the chlorine into the deepest part of the pool at one time. It should turn the water a cloudy, blue-grey color.
Turn on your filter and circulate the water constantly. Try to keep the water circulating 24 hours a day for one week after beginning treatment.
Scrub the sides of the pool with a swimming pool cleaning brush. Clean the sides of the pool, the bottom of the pool, all of the ladders and steps, and all filter or plastic pieces.
Vacuum the pool immediately after you scrub the pool with the brush. Use the pool vacuum to suck up all of the algae that you scrub free from the walls and other surfaces of the pool.
Add commercial-grade algaecide to the pool water in the dosage recommended by the manufacturer. Read the product label to ensure the algaecide will kill the particular strain or color of algae that is in your pool. Pour equal amounts of the algaecide into several different locations along the pool wall to ensure it disperses properly. Repeat the treatment within three to five days, or as directed by the product directions.
Scrub and vacuum the pool every day for one week after you begin algae treatment. Keep the water circulating at all times.
Clean your filter each day. Large amounts of algae will be sucked into the filter after you scrub the pool, so you must clean it out daily to prevent the algae from growing inside the filter.