Autumn is the time to subject your pond thoroughly to maintenance. Remove all died off plants, sprigs and leaves. In this way you will prevent difficulties in winter whereas you will facilitate proper development in spring.
At the end of November leaves have fallen from the trees. Without a net quite a lot of leaves are blown into the pond. This organic material may acidify the pond environment and induces an algal explosion in spring, which checks the growth of plants. During this month you should remove the last died off leaves of the water plants and cut back the marsh plants. If the cover net has not yet been applied, it is time to do so now.
Test the water before the winter one more time for its total JH (joint hardness). Take care that this hardness is at least 8 °GH. You can increase this hardness with GH Plus. During autumn time the water surface of the pond is often polluted and made turbid by leaves, sprigs and dust. This organic material contains nutrients for algae.
Using a good quality air pump during winter months has a number of advantages for fish. Nasty gasses, including CO2, may escape at the water surface. The water will be supplied with oxygen and during a period of frost the water will remain open locally. If necessary, you may additionally feed fish on winter feed. Feed small quantities and take care that no feed is lost.