What kind of model do you have, rs or rc?
1) Do you clean the airline tubing once a week?
Salt creep can get built up in there and restrict air entering the skimmer. To clean the airline tubbing, simply take some ro water heat it up ( I use a 16oz. solo cup) then stick the airline tube into the water while the pump is still running so water can be drawn into the pump and get rid of any salt creep.
2) If you a running the rs model, it is also good to clean the small pvc nipple on the pump that the airline tube attaches to. Salt and calcium can become built up in there to and restrict the skimmer from working to full potential. To clean that, I use a wire hanger and stick in to the opening of the nipple and loosen anything that has becomed built up.
3) Check to see if you have the rubber seal (the pvc elbow from the pump to where enters the skimmer's body) has a tight seal. If that seal is not completely flush up against the body, you will have a lot of bubbles escaping the skimmer. This happened to me, and I just simply pushed the rubber seal as tight as I could against the skimmer's body and that took care of the bubbles exiting the skimmer.
Also how often do you clean the collection cup? For the skimmer to continue to work at it's fullest potential, the cup (especially the interior wall of the cup) should be cleaned 1-2x a week.
As to your second question, I don't believe that the micro bubbles will hurt your fish or corals. But maybe someone else might chime in and be able to answere that for you more in depth.
I hope those suggestions help in solving the problem.
