Preparing tank to transport fish For winter

[Lisak1]

A pond de-icer is not a heater. It's designed to keep an opening in the ice for gas exchange.

Your concern should be both pond depth and water volume. Where I live (Chicago area) a 40 gallon pond would freeze solid - not good for fish. If you have milder winter conditions, this may not be a concern for you. You have a container pond, not a pond pond.

 

[JamieB]

At only 40 gallons, you’d need a very reliable aquarium heater. Better to set up a container that will be big enough for them. Figure 30+ gallons each at the size they are, 60 would be better, which is ideal for a full sized goldfish. If you have the space inside, you could even buy a pond liner, make a wooden frame, and set it up like in your basement, a back room, somewhere with a good solid floor. Preferably concrete floor. Make a temp pond, say 2ft wide, by however much space long you can, and as deep as needed for a volume of about 200 gallons.