We live in upstate NY north of Syracuse and we use a black tarp for a winter pool cover. There is about 6"-8" of water on top of it. With March temperatures way above normal and lots of sun, there is a lot of algae forming on the cover. Is it a problem? Just to illustrate how warm it has been, the average high for this time of year is 46F. Today we hit 79F. I'm tempted to take the cover off the pool, but I know that sub-freezing temps are still in our future. Thanks in advance for any advice.