Snipe, I agree to a point. Years ago it was said to only aerate at night when you have trout in the pond because they will live longer. Only aerate at night when the air temps are below 70°F. The cooler night time temps will put more O2 into the water for the trout. Nobody could furnish temp or O2 data though, they were just saying what someone else said without data. It took 3 years of testing in my pond to prove to me that it was a fallacy. I bought a temp controlled on/off switch, and had the aeration system only turn on when temps were below 70°F. The trout died quicker than if there was no aeration at all which allowed the thermocline set up and keep water cold down at the bottom of the pond. Turning on the system at night mixed the warm upper water with the cooler bottom water and the volume of O2 in the pond wasn't enough to oxygenate the cooler water to a high enough level and the trout croaked.

Without any aeration at all, there was not enough O2 to keep the trout alive below the thermocline, but there was enough O2 in the water right at that thermocline level to keep the trout alive until July 4th.

In another pond a few years ago that was much deeper we were able to keep trout alive all summer long by setting the diffuser 12' off the bottom and letting it run 24/7 along with a surface agitator in the 1/2 acre pond. The O2 levels were high enough in the upper water level to allow enough O2 transfer to the upper thermocline layer to keep the trout alive.

I really think that the people with the hot water in the summer would be much better off going to a surface agitator type aerator than a bottom diffusion aeration system to put O2 in the water. How many fish farms do you see running surface agitator systems vs. bottom aeration systems?

Another thing to consider is that if the bottom aeration system is sized to run 24/7, and someone only runs it for a few hours per day, they run the risk of under-aerating their pond which causes issues of it's own that won't help their situation.