20 Gallon reef

[Canuckgod420]

So I just tore down my daughters tank, cleaned it all up, and now I wanna redo it.

It is sumpless, 3-4 inches of sand, 15-20 pounds of rock and a couple of fish.
Filled with zoa's, ricordia's, and maybe a couple of lps. illuminated with a new wave t5 4x24w.

So I guess to start with there has to be a way to filter surface scum off the water........surface. What I was thinking was creating some sort of divider in the tank to create an overflow area where a heater and pump can be situated to return water. I guess sort of like one of those all in one bio-cubes. Any ideas on how I can create something like this.