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.

What type of diffusers are they (ie, rubber membrane, stone)?

I installed my system around the same time and it's been down for about the same length of time. You've got me curious, to say the least.

Do you have a psi gauge installed on the pump? Would be helpful to know what PSI it is making.

The diffusers I have are like this https://www.livingwateraeration.com/kasco-marine-robust-aire-diffuser-1-15-cfm.html (This is not where I bought them from it is just the first similar picture google pulled up)

I do not. If I don't figure out the problem I can certainly add one I don't think it would be too much trouble.

I'm not familiar with that setup. Is that a soaker hose of some kind or is it a rubber membrane? Does the unit have a check valve? It may be clogged or stuck shut.

If you put 175 psi into your system and only got tiny bubbles at the diffusers...you most likely have a kink or clog in the lines/diffusers, or a break that is letting all you air escape (maybe underground?)

When I deadhead my pump it really makes some odd fluttering noises that are an obvious sign that something is not right. If your pump sounds normal while hooked up to the system and no bubbles are coming out...my bet is that you have a massive leak underground, but not underwater. If it where your pump, the compressor air test would have shown some results.

What kind of pump is the Kasco? Rotary Vane, Piston, Diaphragm, etc.

A pressure gage, as mentioned, is a great troubleshooting tool to have.

Side Note: I would bet that the system is not made to handle that type of pressure (175 psi). Please reconsider putting that kind of air pressure to it again. I would recommend using an air line pressure regulator in the future for that kind of testing. Set the regulator to what the system is designed for (about 10 psi should be safe, maybe as high as 20). 175 psi could be enough to burst something.

Too high of air pressure such as 20-50psi and too much CFM will often damage rubber membrane diffusers; they are basically porous balloons.