Nice tank! Looks great - congrats.
For the background (may be a bit difficult at this point, lol) but I paint the sides and back with the fleckstone paint. Not sure if you remember that stuff, think people used to paint their lamps and stuff to make it look like stone. Basically I tape up the tank, it sprays on really nice. I use the black, white fleck. Looks great as a background. Not to be confused with paint, it actually has texture on it, keeps the lighting in the tank, pretty sweet. I think you can get the paint at walmart even in the craft sections. Takes a few bottles, but super nice effect.