Your power head is to high on the glass it need to be down lower so that when the flow starts it doesn't pull water and air down from the water surface. If the head is strong enough it will create a cyclone and water will be pulled into the power head.
Good luck. Nano tanks are always need constant adjustments for awhile beings the tank is so small. I just stopped having to tweak my 25 gallons equipment now I'm just having to do adjustments on my corals.