Suddenly colder! How does that affect your pond?
In this cold weather it is best to leave the deeper water of your pond alone as some late hatching amphibians may be hibernating and it is best not to disturb them. They will have gone into deeper water that remains warmer longer than the surface does. Any fish in your pond will have gone deeper too and they should no longer be fed.
Adult frogs, toads and newts overwinter in log and leaf piles or beneath stones and plant pots. You could create a rock pile - this should face north to avoid temperature highs and lows between day and night and be sited near the pond or damp border. Amphibians also like compost heaps where they live in a state of torpor in winter so they can rise in search of food on warm days.
Keep the pond pump working but if possible turn down the volume of flow so you do not disturb the deep water temperature.
Consider adding a pond heater to keep an area of surface free from frost and ice. Birds will use your pond in Winter to drink and clean their feathers - essential for helping with their insulation. Do not smash the ice on your pond as this will send shock waves through the water that can upset fish and other creatures. The vibrations can also damage your pond liner. To melt the ice use a saucepan of water to stand on the water surface to melt a section of ice slowly.
Keeping the pond surface as clear of plants as possible will help light transmission to the bottom of the pond and keep the oxygenating plants working well for the longest time possible in these darker days. You should have completed your Autumn maintenance and reduced the amount of rafting plant stem growth across the water.
See more in Tips and Advice: Autumn & Winter in the wildlife pond