Hi Gareth
I would keep the pump and filter running all winter, if you could bypass the waterfall and return the water back into your pond this will help with the chill effect of your pond.
If you are unable to bypass the waterfall then just keep it running normal as running water does not freeze, providing your koi are not to small there should be ok through the winter.
Hope this helps
Regards Shaun F.
Posted on Nov 4, 2006, 6:53 PM from IP address 83.100.251.239