Put in a HiBlow 100 pump and a diffuser in the deepest part of a 3/4 acre pond. Depth at the moment is 9 feet. Pond is 25 years old. Water feeds in during heavy rain from a couple other upstream ponds. Murkey water. No surface algae or heavy vegetation. Clay foundation.
I ran the new unit for 5 or 6 hours yesterday. This morning there were tons of fish on the banks. Some were laying there still getting Oxygen and many others were dead. I saw a couple of my big bass (10lbs) laying there trying to get Oxygen, but tons of Bluegill and crappie were dead. I didn't notice any of my catfish on the banks or floating.
Any tips on why a short duration of aeration introduction caused such a harsh fish kill so quickly. I could smell a bit of 'fishyness' when the aerator was running but not overwhelming or sulfur smell.
Like others have said, you mixed the nasty bottom water too quickly with the good water the fish were living in. It could have caused an O2 problem but the more likely cause of the fish kill was all the nasty toxic gasses of the lower water ruining what good upper water you had.
Ideally you would start up aeration in such an old eutrophic pond in the cool of late winter early spring when O2 would be less likely an issue. But even then you would want to mix the lower toxic water slowly with the upper good water. This gives the toxic gasses time to off gas in small amounts over time at the surface. In the heat of the summer the slow start up just becomes even more important.
