Its a combination of a false bottom/sump.
It started out as an 90 gallon RR Oceanic. I ripped the overflow box out. I then installed eggcrate on 1"PVC spacers and a small piece of PVC to raise the water level to almost the eggcrate. Water flows down to the sump then back up and down the driftwood as a waterfall. (Pumped with a maxijet 600). I left the other bulkhead as a valve so I can drain the entore false bottom as needed.
For the background I used great stuff expanding foam in small layers. (Best tip there is to use gloves and allow time to dry.) I foamed over a few PVC caps as planters, and built up sections to give it more depth. After suffecient time to dry I smeared brown silicone over portions and pushed peat moss/coco fiber mix into the the silicone. I basically repeated that until it was all covered.
Id be glad to answer specifics if anyone has any.