I got a pretty good layer of scum on the bottom of the removable reservoir as well as the neck tube going up to the reservoir, not the neck in the reservoir.
I decided that buildup was preventing any accumulation above it. I pulled the skimmer, removed the reservoir and cleaned it (also had a powder from the live sand dust on the pump that I wanted to clean. I also noticed that my bubble creating horizontal circle thingy (nice name feel free to use it) was pushed off to the side.
After cleaning I put back in, ran it for 6 hours without reservoir (on a more open setting) and now am getting more scum. I am thinking I might have had a layer of sand dust the cone.
Anyway...pleased. It's getting some stuff, but considering there is no food load in the tank...I am happy.