I did a water change today with the same kind of skimmer, i have mine dialed in perfect as long as keep the tank always full,it pulls lots of junk out, and had the micro bubbles at first what i do after starting the skimmer is bend the air tube to clear out any huge bubble in the intake line, because i dont want to move my adjustment,just wend it so NO air is taken in to the clear air tube line then unbend it, i get huge amounts of micro bubbles for about a 3 hours then they go away.