How to keep your fish pond from freezing
When cold weather is spreading across the UK it means ice and snow for many people. Pond ice is bad for fish for several reasons.
Firstly it means that the water temperature becomes very cold. Although koi and goldfish are classed as coldwater fish, they can’t survive at zero Celsius or below and in fact, need a thermal layer of water that sits at 4C under the ice. This means that a pond must be deep enough and still enough to enable that layer to form, or it should be heated.
Pond heaters aren’t designed to significantly raise the temperature of the whole pond - that would be expensive - but they are designed to prevent a small area of the pond from freezing over and hopefully preventing extremely cold water temperatures. Floating heaters are designed to be dropped into the pond before freezing temperatures arrive, plugged in, and it will do its thing.
The second problem with a pond that is frozen over is that bad gases like CO2 can’t escape from the water and good gases like Oxygen, can’t diffuse in. Coldwater does hold a lot of oxygen but its that build-up of gas under the ice that we need to prevent. This can be done either with a pond heater or with an ice preventer, which moves a small area of surface water either by way of a small pond pump or a pond air pump and airstone.
Water continues to move, even in freezing conditions, driving off the gases made by decaying vegetation but at the same time, the water is only moved at the surface, preventing disturbance of that all-important thermal layer.
So by heating or moving the water there will always be an area of the pond surface which is free of ice, even in severe winters, helping your fish to survive.
Check the temperature of the water using a pond thermometer.