HI Kay,Every pond is different as far as the demand for o2 or its (BOD).A rule of thumb for a pond your size is that if you have an area of clear ice then the macro algae and o2 producing plants will produce enough oxygen to sustain your fish and themselves. Keep in mind that in darkness that respiration removes oxygen even though the demand is low there is no sense in risking the fine line. So keep an area of open water or clear ice and you'll be fine. If your diffuser will not keep an 8-10 ft area open then you may have a partially plugged diffuser, if your pond freezes clear and becomes snow covered your system will (should) melt a hole in the ice in time.If I have clear ice for more than a few weeks I usually open the ice up to let it gas off for a day or so.Not scientific but I sleep better that way. I can not STRESS enough to let EVERYONE know to stay off of the ice when you are using this method as you will have thick and thin ice. I see on the Lima Ohio news that a young boy was walking his dog on the ice two days ago and broke through and drown. I do not know if an aerator was involved or not but most unaerated ponds have at least a foot of ice on them in central and northern Ohio. If there is any chance someone may wander out on your pond then leave your aerator off until spring. This is one of the problems with the windmill aerators in very cold temps as they will freeze over and then create thin ice quickly. Even though it states thin ice on most of these windmills it seems to still be a problem. BE SAFE and hope this helps. Ted
