At your LFS they sell backrounds for tanks. Just get your dimensions and they will cut it for you. It's usually on spools in some corner of the store. The heights of different tanks vary, and it's hard to "eye" it, which is why I mentioned getting the dimensions. There is one backround that is black on the bottum and it fades up to a pretty blue near the top... Stay away from it!! After it's on your tank, you can't see the color change. I have a black backround on my tank and I love that stuff. I can change it just for fun if I ever wanted to.