There are a lot of what if's in this question. Too many really. I think you pond is being over turned to many times a day IMO 2 is enough really. In your case your air is so powerful this may be why your losing fish as it overturns way to fast. Typically if your setup was correct for your pond this may not have happened. Although in this colder water most of your pond if not all should have been 100 percent saturated anyway. If you don't have a timer you should get one. I don't think it's from gases after a couple of years your pond isn't that old really. I could be wrong but IMO you have them to much to quick with your setup I bet.

RC

The only difference between a rut and a Grave is the depth. So get up get out of that rut and get moving!! Time to work!!