I try and close as late as I can and open as early as possible. By that I mean keeping the circulation going. I do jack up the chlorine and it's gone in the spring but usually don't have an algae problem. Spring of 2009 I was away for a bit and didn't have the pump hooked up and it did get away from me. Darkest pea green crud I ever saw. I just waited too late. Was cleared up in a few days.
Al