I have a H.O.T. Magnum 250 that is creating a lot of micro bubbles! Itâ€™s making a gurgling sound & there seems to be air trapped at the top of the unit? I have tried various ways to prime it including using a small powerhead to force the trapped air out. I even tried removing that little air tube thatâ€™s on the riser/center section! A friend of mine told me that tube was just to help prime it? Anyway with or without that little tube I still have trapped air in the top! Thereâ€™s no cuts or tears in either of the small round gaskets or the top â€œOâ€ Ring! Any idea on how the air is getting in?