I promised to share the details of this technique during my previous post but didnt manage to do it as I am too busy. There are generally 2 methods to create a background. One is to use a permanent background. Most people use a type of sticky colored waterproof film. The film is then permanently adhered to the back of the tank. This method doesnt enable the flexibility of changing the color of the background and there is no way to illuminate this background.
I chose method 2 which uses colored paper for background. These papers can be removed, replaced and changed anytime according to the effects and needs. The paper can be placed about 4 - 6" from the back of the tank. A fluorescent tube can also be added at the top of the tank, in between the tank and the colored paper to illuminate the background. An additional fluorescent tube can be placed at the bottom of the tank in between the tank and the colored paper if the background illumination is not uniform.
Diagram of setupAn orange background to create a sunrise effect.A blue background to create a blue sky
A white background to create a clear skyThese changes can be made within minutes and you can see the different effects almost immediately. The colored posters can be purchase from any stationary shops and there are a wide range of colors and tones to choose from.
Try it and let me know if you have any other recommendations to improve the setup.