Any reason not to keep aerator on other than electricity cost and wear and tear.
There can be a lengthy discussion about this topic.
Commentary about Dwight's pond situation noted above. Dwight's far north wintery pond is unique. It has been shown to get underground water movement in the basin due to soil geologic structure. There is very likely some oxygenated water that comes and goes into the pond during winter which probably adds some water DO. The circulator no doubt easily and efficiently spreads high amounts of good oxygenated water due to the easily mixed cold winter water into far reaches of the pond under thick ice cover. Thus not a lot of open water is needed in this large 5 ac pond during thick ice, deep snow cover, and long winters. All this works very good for his harsh winter situation.
As Theo mentions running the aerator during winter can cool the water below the normal 39F winter temperature. Most fish except cold water fish are stressed with water temps below 39F. Almost all ponds above the Mason-Dixon line have 39F water from 2ft or 3 ft to bottom. Some ponds will have a thin 3"-6" layer of 40F water
on the bottom deep zone. Bringing this water to the surface where it is chilled by <32F air and can further chill the water and stress the fish to varying degrees and amounts. It all depends.
The current most common opinion at this forum is to keep a relatively small open water area somewhere in the pond. Open water close to shore does allow animals or people that fall into the open water an easy exit from the pond.
IMO the amount of ice and snow cover on the pond has a lot to do with amount of aeration needed between Dec and Mar-Apr. Generally in most but not all "normal" ponds, the thicker the ice and longer snow lies on the ice the more the need for aeration. Years ago I and esshup experimented with winter aeration. He still winter aerates and I do not. I remove snow to about 10%-15% of the iced pond to expose the ice and underlying water to sunshine which allows the phytoplankton to make DO. When snow cover lies on the ice longer than 6 weeks without snow melt off I get nervous. Then I check DO levels and sometimes will start the aerator to melt a hole in the ice to allow degassing and light penetration for the phytoplankton.
Aeration operation times can be variable depending on numerous pond conditions, the compressor type, size and amount of air output of pump and amount of water moved per hour plus other specific topics which is why you will get numerous opinions about winter aeration and also varied opinions about summer aeration run times.
To get customized aerator operation advice there needs to be more information provided about pond specifics. Some of that info you do not have such as depth and dissolved oxygen profiles for your pond. esshup even mentions biochemical oxygen demand (BOD) which is very important for good pond assessment and very few if any people have this measurement. Only the very few pond management companies measure pond BOD or how to measure it. Plus BOD changes with the pond temperature. BOD is usually lowest in winter and highest in summer during highest productivity.
Just about every seller of aeration equipment suggests to run the compressor 24/7/365 especially in southern ponds. They say this IMO mainly to include all possible situations having the aerator doing the most it can do in that pond. Some or many kit aerators and DYI pond aerators are undersized. Ideally one pond water turn over (complete mix) is recommended per day to keep high DO water on the bottom. If the pond aerator is "correctly" sized as a basic minimal unit, it will or should produce 1 turnover each day running 24/7. I always suggest over sizing aerators but this is not economically feasible in big ponds and small lakes. Thus one turnover per 24hr is practical. Initial higher investment of oversizing produces maximum water flow volumes, reduces electric costs, allows more time between pump rebuilds, and lengthens pump life span from using shorter run times.
Generally in my experience, longer aeration run times are needed most based on or if the pond has weedy/high algae conditions that create dead or dying plants at various times, green water, large amounts of leaf and organic inputs, large fish biomass, fish fed 'a lot', old, deep mucky bottoms, duckweed - water meal ponds, when pond is fertilized, has numerous ducks-geese visitors, lower water clarities, the amount of annual sunshine, temperature and nutrient budgets of the water body, etc. All these items contribute to higher BOD and the need for more aeration during summer and winter.
