its not putting any micro bubbles in the tank becasue i have the airstone about 6 inches above the return pipe so the bubbles aren't able to to travel up the return.
i've never seen Calfo's design, but mine is just a basic CC skimmer. the water goes in through the top of the chamber and travels down 6ft to the return while the airstone at the bottom sends the bubbles up.
so far i'm pretty impressed with it. it puts my Kent Nautilis thats in my 125gal to shame. i'll most likely build another one for that tank.
cup after a little tweaking