I am making a "frag rack" out of reef rock that I will either glue or "magnet" to the back of my tank. I have an open spot just under the powerheads that I would like to fill with some color.

Anybody have suggestions for what might go up there? It will be about 4" below the surface, with T5 lighting above it. Also, this shelf will be just below the powerheads on my tank. It's an RSM130D, so there is no way to move them.

So, more than modest lighting, and lots of water movement. Any suggestions from anyone?