the following was posted by lateral line in the diy section sorry cant put link for you to it as i dont know how to do that .
I have always used 2-3 coats of blackboard paint. Clean the glass with alcohol first. I have used it on and off for 40 years and never had any trouble with it. All of my current display tanks, (ie not breeding tanks), have at least the back painted with it, at least on eof them has been with me and painted for 15 years
I have one of these plastic sheet backgrounds at the moment. The water gets in-between and it sticks to the tank. It wouldn't be to bad but it leaves a funny pattern that sticks out like a sore thumb.
Many thanks clunkster, 15 years sounds long enough for me.
because you paint the back of the tank, you never actually see the paint
When the tank's full of water, it looks just like a black background
Bear in mind that you'll find that the tank looks alot darker if you use black paint. But you can always use a different colour. I've seen light blue used to good efffect (smithrc has the blue tanks! )
I went to B&Q and bought a can of midnight blue exterior paint which was 8 quid for a can, was advertised as single coat but I did 2 coats to get a nice thick layer.
I would post a picture but the tanks are facing the wall at the moment, they look the part though so far, should look loads better when lit up with water in.