Tracy:
You mentioned in a previous post about DO readings. What were they at the different depths?
Up here, we stock trout in the Fall for winter and spring fishing. They last until around 70 degree water temp and then go belly up. A client had them still alive in his pond at 80 degree water temp. Pond was 12' deep, 7/8 acre. We ran a Vertex system 24/7 with three airstations, each with 2 diffusers on each. He also ran a 2 hp volcano type surface agitator 24/7. O2 levels were 8.1mg/l that's why the trout were still alive.
Last year another client was able to over summer his trout. Pond is about 27' deep, we played with the subsurface Vertex system for 3 years and finally hit on a combination that worked. He also ran his system 24/7 and ran a 1 hp surface agitator. In that pond we adjusted the bottom aeration system so the pond would set up a thermocline around 12' deep.
In another large HOA pond (18 acres) that had a high phytoplankton bloom and high underwater weed growth mass, the HOA could not afford to aerate the whole pond the first year. We installed a bottom diffuser system in half the pond, using two 3/4 hp compressors. August rolled around, visibility dropped, water temp climbed and the pond had a fish kill. What was interesting is that ONLY the half of pond that wasn't aerated had a fish kill, and the closer you got to the aerated half, the less dead fish there were. The pond was only a maximum of 8' deep, and no thermocline ever set up in the pond, it was strictly a night time O2 crash that killed the fish.
I truly think that it's more about having enough O2 in the water than pond water temp.
When I tried to keep trout alive longer in my pond by only running the diffusers at night when the night time temps were below 70 degrees, it actually killed the trout quicker because the system homogenized the whole water column, but wasn't large enough to raise the O2 levels enough on it's own. If I were to run a surface agitator, I believe I could keep trout for a much longer period of time.
I'd be very interested in hearing what your O2 levels were at different depths of the pond, and at different times of the day.
