Move the dip with the hardscape. Perhaps leave that whole area under the wood void when you stock plants; plant heavily around the driftwood, and left of the tank. That way you're playing with two dynamics for your contrast; closed / tall vs open hardscape, and whatever feeling of the tank, plus a "mysterious" or "dark" cave.
As for the layout itself, I like it. Very minimalistic, looks natural enough. Well done. Also that's a very nice piece of wood.