I’ve already filled the tank and put everyone and everything in it. My stand is dead level. I’m thinking it has to be the plastic on top. I did scoot the stand a little maybe 1-2” in either direction but the floor where it is is level. Stupid me didn’t check before and when we took the old tank off the stand had a distinct rock back and forth diagonally.That would work perfect. Check for level with it sitting directly on the bottom glass. That will rule out a rim that probably is not all of the way flush against the top of the glass.