Preventing a pond from freezing entirely is less about keeping the whole surface liquid and more about maintaining a breathing hole. They key thing to consider here is that without one, toxic gases such as ammonia will start to build up from decaying organic matter, and sadly, these are gasses which can be fatal for fish.
There are many options however to stop your pond freezing over completely, from the cheap and cheerful solutions through to the more expensive;
Use a Pond De-Icer (The “Smart” Choice)
A common mistake is thinking you need a pond heater to warm all the water. Unless you have expensive koi in your pond, then you will usually only need a more simple floating de-icer.
- How it works: It uses a thermostat to turn on only when the water hits freezing, melting a small hole in the ice.
- Why it’s better: It’s much more energy efficient and also cheaper to run than a heater. The key thing it does is that it prevents the pond from turning into what is effectively a sealed gas chamber.
Install an Aerator or Bubbler
Moving water is much harder to freeze than still water, and such you can use this as a trick to help delay your pond freezing over.
- The Benefit: An air pump with a diffuser stone which you want to place about 6–12 inches below the surface creates a constant stream of bubbles. As the bubbles from your air stone or similar rise up to the surface they at to break up the surface tension and importantly keep a hole open.
- Placement Tip: The important thing here is to try not to place the air stone at the very bottom of the pond. In winter, the warmest water is at the bottom. Consequently if you do place an aerator there it will just circulate that warm water to the top, cooling the entire pond and running the unwanted risk of potentially freezing your fish.
The “Tennis Ball” Trick
This option is only really suitable for light overnight frosts. If you are expecting a light overnight freeze, then you should float a tennis ball or a plastic football in the pond.
- As the wind inevitably moves the ball, it creates ripples that will delay ice formation.
- If ice does form, you can then in theory easily remove the ball to leave a small pre-made hole. However, this solution won’t work in a prolonged or deep freeze.
4. What to do if it’s already frozen
One thing you must never do at all is to use a hammer or similar heavy object to try and break a hole in the ice using force. The shockwaves can literally vibrate through the water and kill your fish.
- The Pot Method: Fill a metal pot with boiling water and rest it on the ice. By leaving it here the heat will work to melt a clean hole through to the water below for you.
- The Kettle Method: With this option you can pour hot (but importantly not boiling) water over a specific spot on the surface to gently melt a hole through the ice.
5. Maintenance Checklist
- Stop feeding: One of the key things to do is once the water temperature drops below 10c, stop feeding your fish. Their metabolism starts to slow down at this point, and undigested food will then just rot in their gut and in likelihood pollute the water increasing the toxic gas levels.
- Clean the floor: You should always aim to remove as many fallen leaves and as much general debris as possible before the first freeze – by doing this you are helping to minimise the gas buildup.
- Check the pump: If you have a waterfall or fountain, consider turning it off if the ice starts building up “ice dams” that could divert water out of the pond and drain it.
