I would at absolute bare minimum take the advise that others have also given you. A 1/8" to 1/4" difference along the entire length of the tank is probably not that great of an issue.
As others have told you (And I am telling you too!) it is when opposite corners of the tank are unlevel that you are GOING to have MAJOR problems with your tank.
RISKY! It is somewhere around crazy the suggestion that you "HAMMER" shims under ONE CORNER of your tanks support effectively applying UNEVEN pressure to ONE corner from the oposite corner.
As I said before and others previously stated, it is the opposite side corners front to back that will "twist" the tank and cause the breakage! It is your tank (to break), your money (to throw away) and your house to destroy, so the choice is entirely up to you.
I think that you should either do nothing or if you do, make damn sure that you are shimming BOTH the FRONT AND the BACK of the lower side SIMULTANEOUSLY!
Good luck however you proceed!