post, I believe Cecil has your answer as to what may have gone wrong.Winter aeration can be quite simple and complicated at the same time. When trying to find and maintain the balance of a high percentage of DO saturation and water temps not stressful or lethal to fish without a DO meter it is difficult.I find most winter aeration overdone in the midwest.When your BOD is very high winter aeration is more critical and with a low BOD it may not be needed at all.When in doubt and no way to tell the DO level just keep the snow off of at least 20% of the surface and chances are you will be fine. This is my preferred method. Next method is to have a seperate diffuser (or move your exsisting one) to the shallows and only run when snow cover is present and only as long as it takes to melt off an open area and them let refreeze clear.On ponds where multiple diffusers are present shutting down the majority of them and using one designated as the winter diffuser works too. Caution if you have more CFM going to that one diffuser than it can handle.Either vent off so that you have 1-2 PSI going to that diffuser or install a diffuser that can handle variable CFM (look at the AirPod from Aeration Technologies Inc) as it can take from .5 to 10 CFM.Lastly if you have your only diffuser in the deeper part of the pond and cant move it and cant install a seperate winter diffuser then consider at least venting off most of the air to it, say 1-2 PSI and slow it down. The idea of large open water so a pond can gass off often supercools the bottom of small ponds (8-10 acres and less) and does more harm than good.Winter is already the tough time for fish and over circulation only makes things worse.Most 40F water that is 80-90 % saturated has 10-12 ppm DO in it already and that is twice as much O2 as you need this time of year.Many of todays diffusers can circulate over 4000 GPM with only 1 cfm (20 ft of water)and your pump may have over 4 cfm available.Since proper winter aeration differs so much from year to year I would stay on the conservative side in a small pond.If you have 20 ft or less depth in a 1 acre pond and have open water all winter from aeration and air temps single digits and below you probably have your bottom water too cold (less than 39F) If you have one or two diffusers (depending on depth) running in a 8-10 acre pond all winter probably will not cause any problems as its the smaller ponds that are the most difficult to manage.Use the ice to your advanage as insulation against the super cold temps. Good Luck.
