It is hard to say why you have the bubbles. not enough information provided. bubbles are normally caused by either a leak in the return system and small amounts of air being sucked in and distributed into the tank, water moving too fast through the protien skimmer pulling bubbles out of the chamber and into the tank, too much air to the protien skimmer, too slow water movement through pumps such as a restriction on the intake side or visa versa. oxygen given off by algae in the main. hope something here helps. 1st thing is to determine where the bubbles are comming from. welcome to the site and good luck. keep us posted. happy fishin