b'Some Algaecides are preventatives and Algaecidesothers are used to treat Algae growth. Once Algae has grown in your swimming pool, only a good Algaecide combined with shocking will kill the Algae. Copper-based Algaecides use Copper to treat Algae growth, and are also effective against black and green types of Algae. Copper based Algaecides are good winterisers as the Copper stays in the water longer due to low bather load.35'