Not to hijack this thread, but man, after reading all this I'm a bit worried. I've got my 40g breeder on a workbench with around 3-4" extra on every side of the frame (it's a framed tank). 2 layers of particle board and a layer of plywood on top of that.
Due to the floor sagging while setting it up, I've got a block of wood under the front right leg and a folded up towel under the back right leg. Because of the floor issue, the front right leg is around 1-2mm higher than the others. I believe I asked this before on this forum and was told not to worry about it because it's not a huge tweak.
SHOULD I be worried though? This thing only weighs a max 400 lbs, probably more in the 360 range.