Yep, that's why they make metal shims. Ideally, if your floor is not level, you should make a platform for the tank, level the platform exactly, then try the tank. Guess what? Many aquarium stands are off level all by themselves, so it's back to shimming. What I did on my old 110 was make a plywood platform with 2x4 braces underneath, and put shims between the braces and plywood as needed. (I have an old house that's nowhere near level) Putting the shims in that way meant there was still complete contact between the tank/platform, and platform/floor. It's a PITA, but better to deal with it now than a few months down the road. Funny thing, my corner tank went right on the floor not more than 6 feet from where the 110 used to be, and it's really close to level.