I have a Kasco aeration system with two diffusers that was installed in my pond in June 2017. It has worked well and I have used it 24/7 during the warmer months which are April-October here. I shut it off in October and was messing around today and tried turning it on.

I get no bubbles whatsoever. The compressor is running and I disconnected the hose and put my thumb over the end and I can feel it pumping air. I tried shooting air into the hose with my shop air compressor (175 PSI/ 20 CFM and 200 gallon tank) and I saw no bubbles. I drug the diffusers out from the pond and they are covered in muck.

With them by the shore in a few inches of water I can see very faint bubbles with the air compressor but none with the Kasco pump.

Are my diffusers bad? I tried cleaning them but noticed no difference. I ran out of daylight but tomorrow I will experiment some more.