Seio 820 shooting air

Hey,
I have 2 Seio 820s in my tank that I recently pulled out to adjust and clean because they were really dirty and were pointed wrong and blowing sand everywhere.
I took them both out, unscrewed the ring and pulled it off, including the inner diffuser thing and the prop itself including magnet, I cleaned them both and I adjusted them so they would take less water by spinning the tube part to let in less water..
now one of them randomly shoots out air bubbles, almost like its pulling in air from the surface, but its not. It looks like when the water for my return pump gets a little low and makes a vortex randomly and blows bubbles out for a few seconds.. anyone every have this problem? I think I may have turned the blue knob on the back, dont know what it does, so I am not sure if thats what causing it.. anyone ?

 

The blue knob on the back is for adjusting the flow. The vortex/sucking air means its too close to the surface. One of mine did that cause it was to close to the surface. Just lower it down and the problem should go away. As for adjust the parts to decrease flow, like I mentioned before, thats what the little blue knob is for, lol. The SEIO m820 is maximum 820gph if the blue knob is turned all the way up.