Backgrounds for fish aquariums help lend an aquatic feel to the aquarium and disguise the wall behind the tank. You can use a background in a solid colour, such as blue or green, to resemble tropical water colour. There are also backgrounds with aquatic life like plants and fish printed on them to make the aquarium seem larger and lend to the tropical feel. Some backgrounds are sold to fit the exact dimensions of fish tanks, while others are sold in sheets that must be cut to the correct size.
Clean the back of the fish tank with window cleaner and paper towels to ensure a clean surface for easy adhesion.
Measure the height and width of the back of the fish tank.
Mark the dimensions of the fish tank onto the background using a ruler or other straight edge and pencil.
Cut the background out with a pair of scissors or place it on a cutting board and cut it out with an X-acto knife. If the background was purchased in the correct size, you won't have to worry about measuring or cutting it.
Lay the background picture side up on newspaper.
Apply mineral oil to a cotton ball and rub a light layer of mineral oil to the entire surface of the background.
Line the background up with the back of the fish tank so that the top edge fits underneath the aquarium trim piece. Smooth the background on by hand. It helps to start from one corner and work your way to the opposite side of the tank.
Rub the back side of the background with a plastic card, such as a grocery store savings card, to smooth out any air bubbles. Slowly push the air bubbles out to the sides of the background and wipe up any excess mineral oil from the edges with a paper towel.
If your background comes with an adhesive backing, simply line it up with the back of the aquarium and use a plastic card to smooth it on to avoid air bubbles. You could also try other oil products like vegetable or baby oil, or an aquarium supply, such as SeaView Mounting and Illumination Gel. The background can be applied with tape, but it won't be pressed up as firmly to the glass so the aquarium light won't illuminate it as well.