Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
I use 1/2" thick styrofoam from Home Depot under my tanks.
Many of them have just a shell of Styrofoam, perhaps 2" wide, just under the rim of the tank. The tanks like this are glass, with the weight intended to be just on the rim. My acrylic tanks, where the weight is supposed to be over all the surface have full sheets of styrofoam. This works well to even out the very minor imperfections such as the grain of the wood. It is never intended to solve a wobble. The stand and tank are stable, plumb, level and square before I add the styrofoam.
If the wobble is just the tank, and the problem is perhaps 1/16", when the tank is empty, but it settles and is stable when it is full this might not be a problem. But for a bigger gap, say 1/8" then fix the problem. Get a new piece of wood, or fix the piece you have.
You can start with coarse sanding sheets to knock down the worst area, but do not over work it. Leave it up a bit and shift to finer sanding sheets. If you keep working with the most aggressive sanding sheets you do indeed run the risk of over sanding, and creating a depression where there was a hill.
Stop often to see how it is going.
A 4' level is a good idea. Keep sliding it over the area, and shifting it around in all directions.