Aquarium backgrounds provide visual interest to your fish tank, and three-dimensional, moulded backgrounds provide nooks and crannies in which your fish can hide. They also display your exotic fish against a backdrop like their natural habitat. Three dimensional backgrounds are made of fibreglass, plastic or foam, and are easy to cut to fit the tank or remove.
Remove the water, fish and any equipment or accessories from the tank. This includes water pumps, filters, decorative rocks or plants. Some of the pumps or filters may have been installed behind the background. Remove as much of the equipment as possible without breaking the glass. If a tube is hanging out of the back and can be pulled out, do so. Once the tank is empty and dry, you can begin removing the background.
Remove the top frame of the tank if it blocks access to the entire background. Wedge the craft knife under the edges of the frame and slide it along, breaking the silicone seal. Gently pull the edges of the frame away from the glass to remove it. Work in sections to prevent cracking the frame, as you will want to reinstall it later.
Slide the putty knife between the top of the background and the glass. Most three-dimensional backgrounds are attached to the tank with a silicone sealant. Pulling on the edges of the background will loosen it. Slide the putty knife along the bottom of the background to break the seal there as well. If needed, use your craft knife or the small saw to cut parts of the background away to allow easy access to the seams.
Using a single blade from your craft knife, scrape the remains of the silicone and background from the glass of the aquarium. You should be able to remove all traces of the silicone in this fashion.
Reinstall the tank frame (if you removed it earlier) using silicone sealant.
Use caution any time you are working with a razor blade.