Get a dark pot, and slip your plastic pot inside it. No light = no algae. And take it out to look at the roots when you feel like it.
I don't even worry about algae, moss, or even little weeds that get into mine. I just pull them up when they get too big. In the case of the moss, I pull it up so that air can get down to the roots, when it covers the whole top of the pot.