Thanks for the comments. The background was pretty simple. I carved the basic shape out of styrofoam, concreted over the styrofoam, sealed the concrete with drylok concrete sealer, and siliconed it to the tank. The tank is a 40 gallon long. The Drylok comes in white and I used concrete die to color it. I painted on several shades of grey with the Drylok to get the color the way I liked it.
The rock formation on the right was created by taking a couple of field stones and some cement. I used a few larger rocks to make the shelf like structures and then made pillars out of cement. I used drylok concrete sealer along with concrete dye to paint everything to match.