A: No you don’t actually. They are many water garden owners who leave their koi and goldfish in their water garden throughout the winter season with no issues whatsoever. There are really only two things that you need to do to make sure your water garden is fit to allow fish to winter over:
Does your water garden have a depth of at least 18″?:
This is very important. There are places in the US alone where water freezing depths can easily be around 18″ to 24″. I suggest a minimum of 18″ of depth to be safe, but I am more inclined to recommend 24″ just to be double safe. We want to make sure our fish friends don’t become icicles. In either instance, it’s also extremely important to make sure we keep a hole open in the ice during these cold times, which leads me to the second thing.
Keeping an open hole in the ice during the winter:
During the winter, when the ice forms a solid layer across on the surface of your water garden, there are toxic gases, caused by decaying vegetation or organics, that can build up underneath the ice. This build up can become so toxic underneath the ice that it can kill all of the fish in the water garden. The best thing to do in this situation is to keep a hole open in the ice to allow for these gases to escape. This is actually very easy to accomplish. Using a pond heater/de-icer, such as a Pond Saucer or ThermoPond, is a great way to keep a hole open in the ice. Another way to keep a hole open in the ice would be to use a small bubbler aerator. These will not only keep a hole open in the ice, but will also add oxygen as well! Bubbler aerators can be used all year to keep oxygen levels high.