I dunno, I'll ask next time I see him! haha
It's not literally a solid block, it can be pushed around. I'll take another video. But yeah, not much room!
It's all good questions, most of which I'm still figuring out myself.
From what I understand it's just further broken down so it can be utilized by the coral and other organisms. I don't think it's as simple as filling up your skimmer cup and then dumping that skimmer cup back into the display tank. I think it's more like stealing from the rich and giving to the poor, haha. Know what I mean?
For export, a skimmer is still used and they do recommend some light GFO use. Part of the Triton Elements that are being dosed are feeding the macros. If that goes out of balance you can get algae in the display. I currently have a little GFO mixed in with my carbon.