wow those rocks look sweet in that tank and it looks like alot of weight as well i do see the egg crate on the bottom if you have any concerns you could also go to the hardware store and get a piece of foam like those foam pads but in a larger size to fit the bottom of the tank or you could add a thin layer of styrofoam place the eggcrate on that and then the substrate and those rocks would be an added precaution so to say..