skip the background, all that does is block it from the other side. more plants, maybe a taller rock would help. create zones.
Isn't it up against a wall? What are you missing by putting on a background? A background helps the viewer to focus on what's inside the tank and not on all the equipment hanging off the back of it.
I agree, more plants would help loads. Perhaps you could take the hornwort and bunch it behind the rock, take the java fern bunch and place it on or near the wood, maybe pile the white stones up around the base of the amazon sword, and perhaps try to spread some moss like a carpet in front of the rock. See how those options look for the time being, until you can find more stuff that you like.