Fish should be prepared for Winter by feeding them with a high quality food. As the temperature drops, below 10oc you should stop feeding your fish.
Treat the pond with Pond Guardian Tonic Salt to support the fish as the temperature drops and reduces the freezing point of water.
Cease feeding plants. As the trees surrounding your pond begin to lose their leaves, it is important to stop them polluting the pond water this is best done by using a cover net to keep them out or alternatively remove them manually every day.
Net out half hardy/non frost resistant floating plants which are unlikely to survive the winter.
Give your pond a good tidy up, removing sludge from the bottom or planting shelves using a pond vacuum. Make sure filters and pumps are running well and use treatments like Sludge Buster or Clean Pond Pods to put healthy bacteria into the pond to help with processing waste.
Add an energy efficient heater like a Blagdon Affinity Ice Vent to prevent freezing. When temperatures drop below 4oC in winter, warm water sinks so the bottom of the pond becomes the warmest place where the fish tend to gather.
To prevent mixing the cold surface layers and lowering the overall pond temperature reduce pump flow rates and move them to a shelf within the top 30cms (12 inches) of water in Autumn.