This image shows the concrete-over-styrofoam background before water was added to the tank. I used 1.5-inch high-density blue styrofoam covered with a mixture of Quikrete Mason Mix and Quikrete Acrylic Fortifier. I cut out areas in the back for the filter intakes, heater and power head, so no equipment is visible in the tank. I let it cure for about 4 days in salt water, then another week or so in fresh water. After two water changes there was no elevation in pH so I added gravel, rocks (limestone), and fish. (12/2004)