For the nano cubes you should remove everything in the back. Except perhaps the carbon. Get rid of the bio-balls, sponges, filter blocks, ceramic rings, all of it. It just collects crap and other detritus and will end up polluting your water down the road. A lot of folks put live rock rubble in the back, but I keep mine bare. I believe even live rock rubble could collect a lot of detritus.
:joy: