There's some decent working material there. It looks like you need to bring your lights forward, though. The back glass is lit up all nice, as is the overflow, but neither of those two are things you want highlighted. If you brought your lights forward, you'd light up the rock more, and let the background fall into the shadows a little more, which would make them less of a distraction.
It also looks like you need to make sure the camera is level before taking the shot, to get rid of that tilt. And I'd set the camera a few inches higher, it looks like you're about centered here. This helps create a slightly more top-down look, without ruining the shot with distortion. Other than that, it's mostly post processing.
Here are two shots. The first is the original from my FTS up above, so you can see just how much post processing there really is. I'm reshaping the tank into square, "healing" out distractions, color correcting, adding borders, etc. The second shot is yours with about 3 minutes of Photoshop applied. I rotated it square, brought up the shadows, bumped up the color a little, and sharpened it. More work is done in Photoshop than in the camera, in my experience.
Edit: And yes, that's a 4' tank, standard 120g.