Best Pond De-icer for Koi Ponds in 2021 – 2022: Reviews & Costs

A pond de-icer is a device that keeps a hole open in winter ice. It only heats the area immediately around it, and does not affect the overall temperature of the water or prevent ice from forming elsewhere in the pond.

(Many pond owners also refer to these devices as pond heaters – which isn’t completely accurate. A true pond heater would make the entire pond warmer, which isn’t necessary or healthy for your average backyard pond.)

To understand the allure of the pond de-icer, we need to talk a little about what our finned friends do all winter. While we’re nestled in our heated houses under comfy blankets, most pond fish – koi, goldfish, etc. – are going into a semi-dormant state called torpor that lets them survive the winter outdoors.

In this state, their metabolisms slow, they stop eating and they don’t move around much. They do, however, keep breathing. That means they not only need dissolved oxygen in the water, but the carbon dioxide they exhale needs a way to escape from the iced-over pond.

That’s where many pond owners turn to pond de-icers. The idea is that the de-icer keeps just enough of a hole open in the ice to let bad gases out and good gases in.

It’s a good idea, in theory. In reality, pond de-icers on their own actually do a poor job of promoting gas exchange in the pond. While they will keep a hole open in the ice, they don’t do much to break the surface tension of the water, meaning a lot of the carbon dioxide in the pond stays trapped.

Using an Aerator Instead of – or in Addition to – a De-Icer

Our first recommendation when pond owners ask for de-icers is to try an aerator first. The aerator – with a diffuser placed about a foot below the water’s surface – will push out a constant stream of bubbles that break the surface tension of the water, prevent ice from forming and add some much-needed dissolved oxygen back into the pond.

Unlike a de-icer, your aerator can stay in the pond year-round to keep fish happy and healthy. This is especially important during hot summers, when water has a hard time holding oxygen.

So why bother with a pond de-icer at all? 

If you live in a mild climate, you can likely skip the de-icer all together and use an aerator instead. In very cold weather, though, the de-icer can provide additional peace of mind when the temperature is too low for the aerator alone to keep a hole open in the ice. A de-icer can also serve as an emergency backup in case the aerator fails.

If you choose to use a pond de-icer, only use it in addition to – and not in place of – an aerator.

We like the Pro Air 20 aeration kit for ponds under 5,000 gallons, and the Pro Air 60 for ponds 5,000 to 10,000 gallons.