How much does a pond heater cost for a 25,000 gal/80,000 liter pond?
You are in Melbourne, you dont need a pond heater. It’s unlikely that the pond will even freeze. You cant just heat part of a pond, any more that you can heat part of a gymnasium, any heat you put in will be distributed around all the water. But as long as you are keeping goldfish they are quite safe, even if the pond gets an inch or 2 of ice for a month. Water is at it’s densest when it is at 4C. If it gets colder than that it gets lighter, rises to the top and freezes. That insulates the water, and the ground heat stops the bottom of the pond going below 4C (unless you start getting permafrost forming). Filtering a very cold pond actually makes things worse for the fish as you remove their pocket of ‘warm’ water from the depths. My goldfish has been living in various ponds for the last 9 years, with frosts down to -12C and it’s survived just fine.
