I keep a fuge in my 85g cube. Tried one in the back of a nanocube in the past, and it wasn't nearly efficient enough to bother keeping it online.
I have a sandbed approximately 2" deep and live rock in the fuge along with chaeto, halimeda, and probably some bits of other macros that I introduced and are buried somewhere in there...the chaeto and halimeda seem to outcompete everything I add though. Lighting is 18hrs ON 6hrs OFF on a reverse photoperiod.
The only alternative I've tried was a combo of purigen and GFO on my nanocube, and it actually worked very well...but I prefer the fuge on my current larger tank since I can keep plenty of pods for my (4) wrasses and mandarin goby. I regularly shake out the chaeto in the DT when I harvest it before tossing it in the trash and the fish go into a feeding frenzy
The fuge chamber holds probably 5 gallons of water and is stuffed with rocks and macros on top of the sand bed. I get no detritus build up in there...I run a koralia nano 425 in the fuge and it is loaded with pods and bristleworms that keep the sand pretty much spotless.