OK, got one of those newer plexiglass tanks. I have some nice green algae going, which is not really a bad thing. But, when I used to clean my glass sided tanks, I would just use a single edge razor blade and it would come off straight away, but how do I clean algae off of plexi without removing all the algae from my aquarium???
I've got an acrylic tank (which is pretty much the same thing as a plexiglass tank) and what I do to clean the walls is use toothbrushes! ^.^ Anything abrasive can scratch the walls, so a soft enough brush of something similar will get rid of algae and prevent scratches.