The cold winter

Unlike the summer the warmest part of an unheated pond is normally at the bottom. Which is one reason why Koi ponds should be over 4ft deep. Depending on individual fish, you will notice that when the temperature drops they will lay huddled together at the bottom with their fins tight to their bodies. Some Koi can develop pond sores from lying at the bottom too long and may need attention. If in any doubt, always consult your local Koi dealer.

What do I feed them?

When feeding my own Koi, I tend to wait until the water temperature drops to around 15ºC before changing their normal high protein food to Wheatgerm. I use the sinking Wheatgerm because the water is too cold near the surface to use floating food. Refer to the manufacturers guidelines with the particular food you use. Most Koi will naturally stop feeding at temperature below 6°C. Note that temperatures below 2°C can be fatal for Koi.

What if the pond freezes over?

If your pond happens to freeze over DON'T break the ice, it can shock your fish. Use warm water in a corner to gently create a small hole.

What do I do with waterfalls and venturis in winter?
You can bypass your waterfalls / fountains and turn down your venturis to prevent them from lowering water temperatures and disturbing resting fish. Even though your pond still needs oxygen, cold water holds more then warmer water does.
NEVER turn off your pumps and filters (however, if you have a variable pump, you can turn the flow rate down).