Ok, I'm at my pond at least twice a day and just this morning I noticed one of my 3 diffusers is just "hard boiling" water to the surface!! All 3 diffusers are near each other in my deepest part of the pond and have been working very well for years. 2 of the diffusers are still working properly and see a nice "spread" of small bubbles at the surface put the 3rd is not. Did a hose maybe become seperated from the diffuser?? I have not been able to go out in the boat to pull it up yet. Will it hurt to let it run like that awhile? All 3 lines have their own seperate shut off valve. Should I shut that one off for now? I have duck decoys tied to rope going down to diffusers. I suppose if I pull that up and there is NO hose hooked up I will have to pull the hose all the way back to shore to repair> It is weighted hose and I don't know how else I would pick it up from the bottom of the pond. Any advise what is going on? Am I close??

I think a separated hose is the most likely. If you pull up the offender and that's not the problem, you can see what it is.

Be cautious shutting off the bad diffuser. You may over power the other two. This could cause stress on the over driven membranes. I would just balance the system so that the good diffusers are flowing like you are used to seeing them. Let the bad one bubble until you can get around to it. Once a weighed hose has been on the bottom for a while it gets very hard to pull it in from the shore. You may have to find it at the shore and use the boat to pull it up of the bottom and out of the muck.

I have the "pvc" square type diffusers mounted on a weighted plastic base filled with gravel.

You're not hurting a thing by allowing the 3rd to flow as it is.. shutting it down will, as stated above, cause increase on the other 2 and may be worse for stagnation if you shut it down anyway. At least until you can pull it up I'd let it run.

When I had the same problem it was time to rebuild the motors. Cost is around 150 per motor for rebuild kit.

Tracy, if I'm still getting air thru the hoses why would my pump need rebuilding?

The membranes sometimes separate from the aeration stations after years of use so the air just comes straight out rather than going through the diffuser membrane.

Flame, maybe I miss understood? if you have three diffusers running and then only two and the third is making bubbles but not enough to churn the water then it could be that the motors are not working at 100 %. If it was a leak in the line you would see bubbles at the leak unless the leak is above ground. And I thought I read where the system has been running for two years, and my experience has been two yrs is about the time you get before it needs a rebuild.

No Tracy, all 3 are bubbling real good. But, one act like it is just a open ended hose with the water coming up like a boil instead of the tiny bubbles that are going through the diffuser on the other 2. That's why I think the hose came loose from that one diffuser. I'm not good at making myself very clear! Hah!

I'd guess a ruptured membrane or seal, only one way to find out.
Going forward, it's a good idea attach a nylon rope with some sort of buoy to the diffuser, for just such an occasion.