If you are starting to see some green on the bottom of your pool, algae is probably starting to grow. You should first start by testing the water chemistry. A properly balanced pool is easier to treat. To prevent the algae from continuing to grow, the pool needs a dose of algaecide and shock. Algaecide alone is not designed to kill algae. The algaecide is designed to break down the cell wall of the algae, allowing the shock to penetrate and kill the algae. Not all algaecide and shock are the same. Be sure to use shock with calcium hypochlorite (typically 73% is best) and an algaecide with a higher percentage (typically 50-60% algaecide is best). When adding shock to a green pool, you should add 2-3 pounds per 10,000 gallons. It is best to add the shock and algaecide at the same time during the evening while the pool is still running. Once the chemicals have been added, brush the pool and let the water circulate overnight.
*even if you have a salt water pool, it is still necessary to add shock and algaecide to treat the algae.