Alot Of The Skimmers Have A Venturi Valve Which You Can Close ,so That You Can Eliminate The Bubbles.you Have To Find The"happy Median" Where The Amount Of Air Coming In Creates Enough Bubbles In The Enclosed Cylinder So That The Skimmer Can Work Efficiently In Extracting Ammonia.if Air Adjusted Too High,not Enough Inner Bubbles In Collection Cup And More Bubbles Being Released Back In Tank.if Air Adjusted Too Low-constant Flow Of Water Back To Tank-minimal Bubbles,not Much In Waste In Collection Cup.hope This Helps.