Update to my last post. So it turns out it isn’t my windows.

[Chick-In-Of-TheSea]

Take a piece of paper and try to slide it under your tank. Do this all around the tanks: front, sides, and back. If the paper slides under it gives you an idea of where the tank is not sitting right. If the paper becomes wet, move the fish to a tote on the floor with the filter and the tank water. This is your disaster plan right here. Pick up two of these totes ASAP. Just have them on hand and keep them empty (don’t put “stuff” in them or allow them to become storage.)

 

[Tanked]

If you want to buy time, and possibly fix the problem: Move both tanks closer to the outer edge of the cabinet. Place a single sheet of plywood between the aquariums and the cabinet.  The plywood will help redistribute the weight.  If it doesn't work, the plywood can be used in your new build.