What Do I Do if My Swimming Pool Is Unused a Few Days and It Turns Green?

Adding Chlorine

• Chlorine helps to sanitize the pool and keep the water clear and healthy. Your pool needs a minimum chlorine level in order to combat phosphates and nitrates which can foster algae growth and green water. If you haven't added chlorine recently, you will need to increase the free-chlorine level; some experts recommend a reading of 5 parts per million (ppm) or higher to combat the problem. Have the pool water tested at a pool store for proper levels, as chlorine-testing kits do not always give accurate readings.

Check the Filter

• Your filter may be doing a poor job of keeping the water clear of algae-fostering compounds. If you have a sand filter, water may be simply circulating through the filter without being adequately cleared, due to channels forming inside the filter. You can change the sand, or take the more decisive step of changing the filter medium. There are several natural mineral filters on the market that do a more thorough job.

Heavy Buildup

• Algae grows easily on pool tiles and other surfaces regularly exposed to the water. If you have allowed a film of algae to develop, the best solution is to drain pool, then clean all the affected surfaces with an acid wash to kill the algae.

Organic Debris

• If you've been away for a few days, dead leaves, seeds, bugs, grass and other organic debris may have drifted into your pool, or a storm may have washed fertilizer and other compounds into the water. The result of decomposition is higher phosphate levels and algae growth. To reverse this situation, brush the sides and bottom of the pool and then vacuum it thoroughly; do a backwash to get any remaining loose debris out of the water. Shock the pool with a chemical shock designed specifically to remove phosphates, then backwash again to get rid of any dead and decomposing algae.