Does your Pool look like a swamp when you open it? Do you want to stop this from happening? There are 2 easy things you can do to help stop this from happening. First add liquid chlorine to the pool under the cover. Second is to add a good algaecide to the pool. When should you start to do this………..Now. Call your local pool store or us for more details. As always check with your local pool supply company before you add any chemicals to your pool. Or call us.