Ted, I am running about 12 psi to get 5 cfm down about 400 feet of 1/2" tubing. I do use the same stones as 4GL but I mounted them on a PVC manifold that I built which keeps them about 10" off pond bottom. I use a Thomas carbon vane compressor. I've concluded that I'm very fortunate to have this system work first try. I just picked a set of diffusers that would handle the flow rate of the pump I bought. I sized the pump to be able to handle a larger pond since I plan on expanding it some day. Then I chose an amount of time to run the system that just seemed right and it all worked from day one.

Gotta get back to fishin!