As the weather becomes cooler, you should switch to a wheat germ based fish food such as the Spring/Fall Monster Koi , Koi and goldfish food. This fall diet is easier to digest as they become less active in the cold weather. Gradually reduce the number of times you feed your fish per week.
You need to stop feeding all together when the water temperature is consistently below 50-55 degrees. We stop feeding the fish because the food can remain undigested in the colder temperatures making the fish sick. You may begin feeding the fish again in spring when the temperatures are above 50 degrees.