Step 1: First, clean the surface and bottom of the pond. Leaves and debris left in the pond during the winter will pollute the pond and become a health hazard to koi.
Step 2: Figure out the best way to maintain aeration in the pond for the winter season. This can be done by either manually making sure that ice does not solidify on the surface every day, or by purchasing a floating heater. A heater, preventing the pond from icing over entirely, helps aerate the water and can even keep the water a little warmer for koi.
Step 3: Decide what you want to do with your pump. For example, you may choose to bring it inside for the winter to keep it in good running order. However, you can keep the pump in the pond provided it maintains a strong flow and does not risk freezing. IF you choose to do so, be sure your koi have safe hiding spots because an overly strong current will cause stress on them, even killing them. IF you must take out the pump, you still need to allow for movement in the water for aeration. Therefore, you will need to buy a fountain kit in order to keep the water moving to prevent freezing.
Step 4: Monitor the pond on a daily basis during the winter months to make sure the heater/pump/fountain are working correctly. Replace any parts that break down and ALWAYS make sure the water is moving.
Step 5: Make sure to frequently clean and remove any debris that settles in the pond during the winter. Also, do not overfeed koi in the winter. When the water cools, koi fish’s metabolic rates slow down accordingly. Therefore, they do not need the same amounts of nutrition that they would normally need in warmer months.