...just painted the back of my new tank, very quick and easy. I just did as Steve_89 said, used a spray pack of matt black, a light coat to start with, it dries very quickly - within a minute or 2, then a couple of coats over the top. Took about 15min all up including the masking and turned out great!

check out my personal gallery for pic's, my 25 gal backround look's the most stone like...