I purchased one these about a week ago. It stopped producing micro bubbles into the display tank within a week for me which is a huge improvement over the older model which never stopped with the micro bubbles and I had to use filter floss to block the bubbles between the skimmer chamber and the return chamber on an ongoing basis. Seems to be a much better skimmer.
I have two running, and they took about a week to break in. I would close the air supply and then open just enough to start, lowering the collection cup as needed. Also, make sure the pump is seated correctly below the bubble plate diffuser.