Cover pond with leaf netting to keep out leaves and debri and birds of prey. Check your fish carefully for parasites and bacterial infections and take appropriate action before winter close up. Do not let pond freeze solid, always keep a small area open to let the gasses exchange Example ( floating pond heater) or aeration pump with diffuser stone. Do not chop a hole in the ice, because the sound waves can affect your fish health
Temperature of water in pond – When water temperature is above 55f koi will swim and start to feed normal. When temperature falls below 50f koi begin to slow down and hibernate. At this point do not feed. Provide a natural refuge for your pond fish while they are inactive by placing large diameter plastic or terra-cotta pipe 6” wide or more.
Remember shutting down your pond pump and filtration systems in the winter months vary due to what type of pumps external or submersible. Filtration systems also vary to what type of filters whether they are in the ground filters or above ground systems. If your system requires shut down for the winter months, make sure water is drained in plumbing lines and filters and pumps.