Conner,
What did you use to seal the joins? I can't see any of the red or blue pvc glue. How long did you wait for your clue to dry before putting water? some glue will dry/hardern in a matter of mins but takes a day or so to fully cure.
Im guessing its silcon that your using if its that stuff on the left return. Doesn't look like the right has any?
I can't really tell but from the pic it looks like the micro bubble is comming from the right return only? If this is correct I would check the pumping from the right to where it joins the left. Air getting sucked in between the after the split to the right return.
I can't see a skimmer in the sump so its not the micro bubble from the skimmer right?