I don't cover my pool anymore and when the ice melts I just keep an eye on the water. Watermom was right in that I did have a slight algae bloom when the water was a little above 40 I believe. As for equipment, I wait until the temps won't hit the freezing damage point before hooking things up. Solar stuff won't get water until I'm REALLY sure they won't freeze. Be aware that on clear cool nights the solar heaters will become good radiators of heat and freeze first. With a clear sky they are looking at cold space. Before you fire up the equipment, if you have an algae problem, you can add chlorine (bleach or whatever) and circulate by any means, even a simple submersible cheapo pump.
Al