Are your microbubbles all the time, or just after a filter cleaning? My fluval will do this, but only for about a day. Then stops. I attribute it to cleaning the filter sponges.
I have an XP1 and my turn valve (to make flow faster or slower on the spray bar). There was a cap on top that was letting air in. I took it off and blew in once side and held the other side closed and alot of air came out. So I went out to the work bench and slamed it down a few times to put the cap on tight. Did the blow test again.. no air.
There is either air in your system or you didnt prime it correctly.