I think one of the hardest things about doing a nice aquarium is what to do about the background. I’m frugal, so I’ve used black plastic trash bags taped outside and then plants and decorations to take emphasis away from the fact I’m using a trash bag.
Perhaps you want something a little more… professional. 3D aquarium backgrounds are a great choice, but most are insanely expensive. I just ran across some really beautiful ones on BangGood that cost one heck of a lot less than the other ones I’ve seen.