I have a standard size 90gallon in a basement. The tank sits in a corner, around 8" away from all walls. The floor is cement, with a thin carpet over it. The stand itself is a sturdy wood sedona, before the aquarium was placed on the stand I checked to ensure it was stable at all corners, also the surface at the top is flat, the aquarium is resting on the stand on all corners.
However, the rear left of the aquarium is exactly 3/4" lower than the front right corner. It's visually a noticable difference.
The aquarium itself I've used for many years, and have never had any problems with it. In fact, in my old basement it also suffered from the same "leaning" (though at the time on an iron stand). But the condition wasn't as severe.
Anyway, my aquarium is currently cycling (FOWLR
) and though it would be a huge PITA to tear it down to shim it (considering my work schedule for the next month is 14-hr days, 7 days a week.) I could pull some allnighters if there is a real possibility of a leak.