Don’t worry about the small bubbles stuck at the top. They will not be a problem. They may or may not come out on their own.I can barley see any water movement at the 90 pvc elbow , and no bubbles sucking to this 90 PVC .
I do hear the pump chop co2 from time to time (when the co2 regulator is on) , and can feel the water flow through her pipe....but visually , she doesn't suck almost no bubbles from the top of the reactor