The steel wool scrubbers can scratch your glass so you need to be very careful using them. I have found that I can remove almost any amount of buildup using a non-scratching Scotch-brite. They make green ones that will scratch and blue ones that won't. Somewhere on the packaging it will say. I used one up cleaning a 120 gallon that I had let go and allowed to just dry out on its own from being a full tank. That was in an earlier life when kids interfered with almost anything I tried to do. When I decided to set the tank up again, you can imagine what it looked like. It took about 2 hours of hard scrubbing with that sponge just damp but it did the trick. On a smaller tank, I set it up at a steep angle outside so that no more than a gallon or two can collect in it and go to town on it with a scrubber and the garden hose. I can usually get a tank looking good enough to fill in under an hour doing it that way. To get the side that has been sitting in a puddle while I scrub, I just flip it so the other end is up and I can scrub it rather easily.
