People clean the algae off of the greenhouse walls?? WHAT? hahaha.. Just kidding. We have lexan panels on our greenhouse and I give the walls a high pressure rinse every now and again to break down the algae. I never really remove all of it as it adds some shade. Bleach water will both kill and help remove the stuff if you want it gone. Keep the fans going though as the bleach gets to be overwhelming after a bit- at least to me.

cheers,
BD