DIY: Concrete Aquarium Background

To prep the tank, empty it, wash it in a mild bleach solution, wipe it down with rubbing alcohol and allow it to dry. Gather several sheets of polystyrene foam, a tube of 100 percent silicone, a bag of Quikrete quikwall, Quikrete concrete acrylic fortifier, several colors of concrete pigment and a single-sided razor blade. You may want a hobby heat gun, a hacksaw blade and a surform shaver tool to help create a more realistic landscape.

Carve your background out of the polystyrene foam. Carve a number of formations that will fit together, checking to make sure they fit into the tank. Consider making small caves or crevasses for your fish to hide in or platforms where you can place plants. Leave a carved space behind your formations for any pumps or filtration systems you would like to hide. Make sure you create a good sized cave leading into the space so the pumps get an adequate flow of water. When it's all put together, your background should be a few inches under the water line for the sake of the pumps. Use a sharp tool like the Surform shaver to make all of the edges rough, both for a natural look and to create more surfaces for the concrete to adhere to. You can use a hobby heat gun to melt the surface slightly as well, for a more natural appearance.

Once you have your template the way you like it and have double-checked that everything fits correctly, you can secure your creation inside the tank. Apply silicone liberally to attach the pieces to the tank and each other. Layering the polystyrene foam will create a more dynamic look than solid sheets.

Mix the Quikrete according to the instructions, replacing half of the water with Quikrete concrete acrylic fortifier. Use a 2-inch paintbrush to apply the concrete to every foam surface. Wipe the glass around the structure when you're done to remove any misplaced concrete. If it has dried, use a razor to scrape the glass clean. Once everything is coated, allow it to dry for 24 hours. Apply a second coat and again allow it to dry for 24 hours. Apply a third and final coat, using a turkey baster to fill in any remaining gaps between the glass and the concrete. You may want to spray paint or cover the back of the tank to hide the polystyrene foam from the outside. Spritz the concrete with water six times a day during the next three days to cure it and prevent cracking.

To ensure the tank is safe for your fish, fill the tank with water and allow it to soak for 30 days, draining it and refilling it once a week. This will leach out any harmful elements, such as magnesium and calcium, and prepare it for occupancy. After 30 days, replace the water again and add substrate, plants and features you want in the tank. The tank is now ready for its first occupants.