I bought a used 220 gallon tank with a home built steel stand. The steel stand is 2" L bracket all around the top. Then on top of that is 1/4" plywood, 1.5" of foam then the tank. The tank sank into the foam at the previous owners house when it leveled itself out. Now at my house I'm about 3/8" heavy out of level from front to back. I'm wondering what option would be better. I could get another 5/8" sheet of foam and put it on top, but when I put the tank on will it break the new foam in the spots the old foam has already sank down? Or I was thinking of shimming between the metal stand and plywood. I'd like the shim idea better because I can do that without help. My question is if I shim between the metal stand and plywood will it cause stress to the tank? Once I shim from the front level I'll add shims down the side and through the middle so it's not floating.