Pond Boss Forums AERATION Should I aerate? Should I aerate all year?

CT- Pluses and minuses of running your aeration system IN WINTER in your specific pond situation.
Since your pond is fairly large with an maximum depth of 18 feet and your ice cover is usu 3 months (sometimes 4 mo.), I think you do not have to run your compresor during winter PROVIDING 30% to 50% of your snow cover is removed within 2 weeks of a snow fall. Snow cover for 3-4 weeks is now a point for concern for oxygen levels in your pond situation. DO situation near the bottom can be easily checked after 3-4wks of snow cover by fishing (see below). Oxygen is first lost at the bottom and then the decrease progresses upward from there. Since your pond has a lot of water volume due to the deepness 18 ft. the 'bank account' of dissolved oxygen is larger than say a pond 10 ft deep which would have less water volume and overall DO.

Snow is your enemy during winter. It limits light penetration thru the ice. Without light the phytoplankton cannot make oxygen and everything aerobic ('oxygen breathing' including plants) uses oxygen during darkness. In winter the oxygen is not consumed nearly as fast as it is during the warmest water periods. Three days of darkness in summer would probably be enough to kill fish.
Water under fresh/first ice cover has about twice as much oxygen in it as when the water is 80-85 deg. Thus it can last a lot longer before it gets to the point where the low levels are killing fish. How long the oxygen lasts is primarily dependant on how much dead material from autumn is still present to consume oxygen thru bacterial and benthic animal respiration which is quite low compared to summer levels but still measurable during cold water periods. Dead material in your case is primarily leaves which is a major concern. Leaf input amounts in relation to water volume is the most important factor for DO loss due to decomposition in your case.

After removing snow from ice in winter the phytoplankton can replentish the oxygen levels to saturation in about 8 - 10 hours of sunshine.

An easy way to check your oxygen levels near the bottom is to see if you can catch fish on or very close to the bottom. If you're catching fish near the bottom adequate oxygen is still there and aeration is not necessary.

Winter Aeration Negatives.
Cost of electric and wear & tear of compressor parts.
Aeration during very cold weather brings warmer bottom water to the surface and supercools it which causes more stress on your fish. The near bottom water has a little geothermal warmth to it and provides a slight warm water refuge for the fish providing oxygen is also present in this water. Disrupting or eliminating this refuge stresses them. Winter is the most stressful period for fish in the north. Aeration is not necesary if oxygen levels are adequate. Oxygen will be adequate if snow is removed (shoveled or wind blown) from 25% or greater of the pond surface; preferably lengthwise across the pond.
If snow cannot be removed from the ice the air flow from the compressor you have (4.2 cfm) and resultant bubbling can fairly quickly (10-16) hrs. open a hole in the ice (8" to 12" ice thickness) to allow light to rapidly stimulate oxygen production from phytoplankton. The open hole will increase depending on how much you run the compressor, amount of sunshine and the air temperature. The bubbling of the diffuser will also add some oxygen to the water but a small percentage compared to the oxygen produced by the phytoplankton. Oxygen production in the open water area and distribution of oxygenated water via the aerator currents should provide an oxygenated refuge during low oxygen lengthy, deep snow periods. Lengthy deep snow periods are probably rare in southern Indiana. Note this oxygenated refuge will be somewhat supercooled & the fish will probably seek the most comfortable location of temperature vs oxygenated water.