Hi Bruce,In looking over your numbers can you tell me at what water depth you took a reading for your DO level after the 8gpm horizontal nozzle was installed.I also see that the 12 gpm well water being infused into the pond would be a high percentage of new water (approx 11%)I have never had a crash that took all the fish out that had a system with the ability to turn the column over at least twice per day unless the crash was due to chemistry.Even then the mortality was perhaps 25%. Do you know what your airlift device is turning. I ran the lifting ability numbers on a few models of diffusers and see that even at 1800 gpm with 1 cfm in 5 ft of water you would get "17" turns and I would think this would lift beyond any need.Even 85F water at 80% saturation would of provided 6 ppm of DO.Perhaps placing a diffuser in shallow water 3-5 ft and regulating the airflow would provide you with the same results.Im also wondering if in this small pond that even with horizontal aeration that a lot of the cooler temps in the 12ft areas wont be lost as any type circulation will effect the bottom water to a degree. Cooler water on the bottom is great in theory when is has a way to receive and retain DO and this is one of the sacrifices with any type of aeration system,you will warm the bottom.With bottom diffused aeration warming the bottom the most.Normally this is only of concern on the cold water fish types. My concern is always that the benefit of cooler water on the bottom for warm water fish may not outweigh the many benefits of a warmer more aerobic bottom.Your DO drop at night of 4.5 range is a level that I see as a minimum and is not difficult to acheive in most cases.Your dieoff of micro and macro life must of been massive and hopfully will not occur again in that fashion. If you wanted to centralize a diffuser but the depth is excessive consider floating the diffuser at different depths as they are easy to suspend.I highly encourage pond managers to know their cfm input at different depths (pressures) and what those turnover rates are at those different depths.Also to be considered is that what we find may work in a .09 acre pond will not in a pond twice that size by just simply doubling the inputs.This is what makes pond management the graet fun that it is.Ted
