Pressure points will be caused by the rocks if you place them directly on the glass, this can cause cracks in the future. You don't want to place the rock structures on top of the sand because cichlids dig and eventually the rocks would tumble down, possibly breaking the tank. The solution is to take a completely empty tank and place either egg crate or a few thin sheets of styrofoam on the bottom glass.
Now when you place the rocks in the tank there is some padding under them and this dispurses the weight of all those rocks.
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