[header] How to determine which pool algaecide and pool clarifier is best for your swimming pool [title] Add preventative algaecide to your swimming pool on a weekly basis if you regularly experience problems with algae growth. [step] If you have never had an algae problem in your swimming pool, there is no need for the algaecide. [title] Realize that if you have algae right now, you may need to use an algaecide. 
[step] Some algaecides are preventative and others are used to treat an algae problem. Once algae has grown in your swimming pool, only a treatment algaecide combined with shocking will kill the algae.