I have to say I agree with all the other comments. I love the plants and fish, but I keep looking at the background to see if a fish is in the rocks. I would go with a dark Blue or black background to make the plants pop more.
You might want to look into the future a bit here. That background is pretty realistic and gives the illusion that the tank is deeper than it is. Once the plants grow in and fill up most of the background, it won't be so distracting anymore. A couple of open spots in the back showing the rock background would look pretty nice.
