This is the perfect time of year to begin preparing your fish pond for the winter months. Goldfish and koi are very hearty and can survive in your pond even if the temperature gets as low as 0ºC. Just make sure your pond is at least 24 inches so your fish don't get frozen solid. Fish can be resilient but they are not invincible! As the temperature drops, these amazing creatures will go into their natural dormancy, or torpor, needing mostly oxygen rich water to survive. As you prepare, there are a few steps you need to take to make sure your koi or goldfish have a safe winter season and your pond has a healthy start next spring.
Once the water temperature drops below 18ºC, feed your fish a fall food such as Profishent, Legacy, Tetra, or Hikari. Feed the fish gradually less food as the temperature drops, stopping feeding altogether once the water temperature stays below 10ºC.
Put a net over your pond to keep leaves from getting in. You could also consistently skim your pond. Leaves left to decay over the winter season will lower water quality and oxygen levels.
Make sure your pond is free of debris or sludge with a fine mesh net or pond vacuum. Trim dead leaves off of plants and get as much dead organic matter out of the pond as possible to minimize decomposition over the winter months. Decomposition releases harmful gasses over the fall and winter, depleting oxygen levels potentially harming your fish.
Add Beneficial Pond Bacteria such as Easy-Pro Pond-Vive Pond Bacteria to help break down decaying matter and help your beneficial bacteria recover after the long winter months. This will give your filter a boost and make keeping your water clear in the spring and summer much easier.
Make sure your pond is getting enough oxygen with and aerator or air stones. Putting these in a shallow part of your pond will help keep a small hole in the ice allowing harmful gasses to escape and more oxygen to enter.
Heaters are also a reliable way to keep your pond from freezing over. They float along the surface and prevent ice from forming. It's a good idea to use these to ensure your pond will not freeze over, especially if ice on your pond gets to be an inch thick or more.
Once spring weather hits and your water warms, start feeding your fish again and give your pond another boost with some beneficial bacteria.