Pond is about 3/4 acre and about 8' in places. I think it had a heavy fish load and I do feed 3 sec twice a day sometimes more if I'm out there and just want to see fish. Pond has always been healthy and fishing great. It's about 5 years old and never a problem except treating fa with copper sulfate and killin some cc a while back. 10"+ cnbg, 5lb+ lmb, and some really large cc. I use some beneficial bacteria to help with over fertilization "pond clear" & "Eco boost" since I mow and have horse pasture run off. I also use that blue dye, the name slips me. I have been doing the same this whole time and no probs. Had to be the major restart of the aerator and stratification.
How long ago did you kill the FA? Do you have an algae bloom? And if so what is the water clarity?
Yeah obviously the shut down and start up is a factor but i believe you have other things going on. I can't believe a pond with a normal load of fish would go anoxic in tbe deep water that fast with out other factors in play. I know mine wouldn't and i have a heavier load than most as border on an aquaculture load.