Outside the Tank

• The easiest way to add a background to your aquarium is by hanging a thick piece of colored paper, cardboard or thin sheet of wood on the outside of the rear glass panel with tape. Any type of decorative paper or foil can be used if it blocks light from shining through. Most people use underwater scenes or a neutral black, blue or gray color.
  
  A more permanent method is painting the outside of the rear glass panel so no light shines through. Usually dark flat colors work best. Several thin coats work better than one thick coat. Spray paint works to avoid brush strokes, but be sure to mask off the rest of the glass that you don't want to get paint on. Because the paint never comes in contact with the water, any paint made for smooth surfaces will work.
  
  

Inside the Tank

• There are several ways to build a background inside the tank. One method is to lay the tank on it's back, cover the back glass panel with a thin, even coat of silicone aquarium sealant, then sprinkle sand and small pebbles over it. When the sealant dries, the excess sand is knocked off and the back will have a natural rock wall look.
  
  Other more complicated projects include strategically arranging rocks, driftwood and ceramic caves, all glued together with aquarium sealant so they cover the entire back of the tank like a puzzle. Gaps can be filled in with sand and small stones or by a painted black background on the outside of the tank glass. Avoid using shells, because they tend to dissolve over time. The benefits of this method is that it can be removed and replaced at a later date. This also creates more of a sense of depth than the other methods. Incorporating rocks and wood allows you to grow plants and moss up the back wall, making it come alive.
  
  

Aquarium Safe Supplies

• If it goes inside the tank, you have to make sure it's safe for fish and plants. Any gluing can be done with standard aquarium sealant like the type that already seals the glass at the seams. Most rocks and driftwood purchased from reputable suppliers are suitable if washed with clean water or soaked in bleach water to disinfect them first. Avoid metals because they will corrode and contaminate the water.