I was getting a ¼ - ½ inch bubble every half second or so entering the skimmer (this is with tap water). The bubbles became less frequent after a few minute of testing. I’m sure that the bubbles I’m getting are ok, and will not affect performance.
I think it’s more about getting the correct flow thought the skimmer and the right amount of air. My skimmer is plumbed directly to one of the two overflows, no tees and no valves to the skimmer. I do have a valve on the other overflow so if I want to increase flow to the skimmer I could just close it a little. My return pump is pushing between 700 – 750 gph to the tank so I’m getting 350 – 375 gph to the skimmer. The max rating for my skimmer 475gph. So at 350-375gph it is running a little slow; however I think this is a good thing.