Slanted panes

[Aido97]

So I have had the same tank for 7 years now. Its a great tank and I am really enjoying it. But, today I noticed that the front and back pane are slanted ever so slightly in the front direction. The slant is not caused by my floor, my floor is slanted slightly too, but my floor is slanted in a different direction to the two panes. Its a TINY slant, but enough to get me worried.
So my question is, what do I do in this situation?

 

[RadMax8]

I would make sure everything else is square. Are the from and rear panes sliding with respect to the side panes? If so, you might need to replace the tank. If everything is square, I would check out the floor. Is the tank on carpet? Maybe the pad is letting go. Keep in mind, aquariums get HEAVY when fully loaded!