There are many implications of the cool weather approaching and the often unstable weather patterns. Learn more by clicking on the title or picture.
With the cool weather approaching you have to adjust how much you feed your pond fish based on the weather forecast. Reduce the amount you feed if the weather is going to be cooler. Don't change the feed - just the amount fed.
Your biofilter will also ‘feel’ the cold and reduce it’s activity and this is another reason for reducing feed.
You should also be checking the pH and KH of the water to ensure it remains stable over the winter, at least once a month.
Make sure you remove all the accumulated, dead and decaying matter from the bottom of your pond and from the filter chambers.
If you bring your Koi in for the winter, or keep them in a smaller environment, then the addition of vitamin C at a rate of 1-10mg/L is also helpful to boost your fish’s immune system and will help with wound repair if they sustained minor injuries. The use of vitamin C is impractical in most Koi ponds because of the amount needed for the size of the pond.
These recommendations by Dr. Richmond Loh, The Fish Vet, Perth, Western Australia