I got my 75 setup with 100lbs of sand, around 20 lbs of driftwood and filled it up and the water level is about a quarter inch difference from each side length wise, I spent 20 min banging shims in on the high side and it doesn't seem to be doing much, the shims are thick enough and I have them spread out slowly banging each one to try to distribute the weight, so how majorly important is a perfectly level tank and should I just keep shimming until the whole shim is under the tank?