The second tank has a layer of polyurethane foam, then portland cement applied to the foam. I would have spent more time building out the cement to make it less flat, but with all of
the fish from the 120 gallon tank stuck in the 30 gallon sump, I was in a hurry to get it set back up with the new tank. With the polyurethane foam, it would not crack the glass like
the first cement tank. You can see the overflow in the back right corner. There is also a natural looking cement floor under the sand.