Unless your aquarium is acting as a room divider with it being visible from both sides there is a chance you will be adding a background to your fish tank. Backgrounds have been in the fish keeping trade for many years now however more recently it has become more common to install a 3D background in to your fish tank. These are often made of polystyrene or poly resin, the main difference being that resin backgrounds allow you to install equipment behind them easier and are possible to install in an aquarium with water and fish already in it.
Backgrounds on fish tanks are a great idea to ensure that fish do not have reflection from the glass and it is recommended that you have background on at least 2 sides of the aquarium to ensure the reflection from the glass is kept to a minimum. The only pitfall of a 3D background is that is takes up physical space within the tank itself so there’s less space for fish and water however on the upside they can be extremely realistic and make your aquarium really stand out and give it more of a realistic and 3 dimensional feel.