Get shims... They even sell the composite ones that will not get effected by water... Shim the corners first and get the tank level in both directions. then fill in around the stand with shims to make sure that you are not supporting by just the corners.
Cool thanks guys. It's only a 55g. I figured I could just shim it. Just wasn't sure if I had to shim the hole side or not.
However I'm going to ask the landlord if I can unbolt the house and shim the foundation. I want to do it right. LOL
It looks like if it isn't level it would be leaning towards the front of the tank. Which I would have to shim the front. And the tank is going to be on (unfortunately) carpet in the living room.