I am not an expert and this is just my opinion, but here goes. I have a 29 gallon FOWLR
and run a five gallon WET/DRY filter. This means that my overflow goes into a 5 gallon bucket filled with bio-balls then drains into my sump, which is a ten gallon tank that houses my skimmer and my pump back to the tank. In short your "micro-balls" are supposed to be wet but not submerged. The schematics of just a single tank are much more complicated, but possible with a lot of drilled plexiglass and silicone. I have found my approach much easier and cheaper.