Glad you don't mind ?'s
One nice thing about this skimmer design is that there was no bubble return at all into the tank it was running on.
After you added the air and adjusted the water level again where did you leave the final level of water and bubbles sitting when you let it run for a while? Was it in the first riser or the second and how far up in the riser.
I think I need to set it up on my tank at home and just let it run for a couple days and see what happens.
I cut the center injection riser down to about 2.5" When it was about 5" long I was getting a clear band of water at the bottom of the first riser.