Have u tried vinegar? If it's calcium deposits vinegar should take care of it. If not, you could always cut the glass out and replace it with another sheet. although the lost light would probably be negligible.
Hiking works, just be sure to do the acid test on the rocks when u get them home. If it fizzles, it probably won't work.
is the floor not level to begin with? in all my years of keeping fish, I guess I have been lucky, in the fact that I always had Tile floors, or some kind of built in shelf to place tanks on. On tile, if needed I would usually just use a shim of some kind.
Hopefully someone with more experience in the plant department can answer that one.
hope some of this helps