I have only got one year of aeration experience under my belt, but my deciding factors on the hours that I run the systems is based on outdoor air temps and water temps. Being in Missouri and only having a 1/4 acre pond, I worry about over heating the pond water in the heat of the summer. So, I take temperature reading at 18" down and at 7 foot down and compare to the outside air temps. It's a bit tricky when the air and water temps are in the 80's, meaning that about 85 water temp is what I consider borderline too hot. I will gradually start the air up in the spring to 24 hours a day until the water temps get to the mid to upper 80's then start cutting it back to only run at night so that it reduces the amount of heat transfer during the day. Once fall hits, I start adding aeration back to the day time hours when the outside temps drop below 85. This period is a very short, it seems like fall comes in pretty fast and may not be yielding much benefit. Then as mid fall comes in, I reverse the thought pattern and try to maintain warmer water by reducing nighttime aeration. This can happen pretty fast too and benefits are questionable as well.

Note: the heating effect comes from the moving of the water to the surface where it can become more exposed to the sunlight/hot air temps (or cool night air depending on the season). More movement equals more heat transfer regardless of whether we are considering heating or cooling of the pond.

The reason I really question the benefits with the above concept during season transitions is because changing the aeration time schedules certainly affects the fish's feeding habits and their willingness to be caught on rod and reel. I ask myself if the fish would be better off with one fall time aeration change (like band-aid removal) compared to 2 or 3 gradual adjustments over the the coarse of the month?

Being in Nebraska, I suspect 24/7 summertime aeration may be what is called for and spring and fall transitions could likely be more abrupt compared to Missouri.

I have read that running air lines under ground is a good alternative compared to running electricity, but I have also read about condensation in the lines being a problem if the lines are not run with proper grading so that water condensation buildup can be avoided...frozen lines are not good.

Fish on!,
Noel