Finally got fed up with the tendency of my xp1 to collect air and blow microbubbles.
I called aquariumpharm and they taught me a fix that works!!!!!
take off the filter top. turn it upside down. On the same side where the power cord runs in is a black cap sort of ...using a flat screwdriver pull the cap out 2 mm , to allow air exchange between the impellar and the atmosphere.
no more bubbles!!!!!