You know, it is funny. We used to tell people that you didn't have to worry about algae in cold water. But, we found out that isn't always true. Al (Poconos) has a really cool picture of algae under ice in his pool. I think he already has it posted here somewhere on the forum in another thread, but not sure exactly where. He also mentioned to me the other day that he sees a little algae in a couple of spots in his pool and he still has ice in his pool --- something like 7 inches worth I think. Weird! Maybe he can dig up that picture and link it here. It is a really neat picture.