i had micro bubbles real bad. first, shake the return pumps a few times. i think perhaps a "air lock" is created in the pumps, causing some bubbles, second, your return jets, (i have 2 locklines per return lines). i will place my finger over one return, forcing all the water out of only one hole, and will notice alot of bubbles comming out, again another air lock. third, in the pet/fish store, you can find some filter in bulk, its blue on one side, white on the other. kind of looks like ac filter. i cut it to fit over my return pumps in the third chamber of my refuge. when the water comes down from my DT, it goes through my protein skimmer (bubbles), second chamber (cheato will "stain out" some bubbles) to the third chamber where it get send back to DT. i cover the the third chamber with this cut-to-fit filter, and no more bubbles!!! good luck.