Written by By Mike S. from the Drs. Foster & Smith/LiveAquaria Technical Support Department.
With a pond depth of 3 feet or more, you can safely keep fish outside during the winter months. When doing this, it is critical to keep a hole open at the surface. As leaves, debris, and fish waste decay in water, it creates toxic gases that can be harmful to the fish if trapped in the pond. Keeping an area open in the ice will allow these gases to escape, as well as help add new oxygen to the water.
Pond owners will typically utilize air pumps, water pumps, or de-icers during the winter to keep the surface from completely freezing over. In colder climates, pond de-icers are generally a better option, as water and air pumps can cool the water and affect the condition of the fish.
Both floating and submersible de-icers are available for pond use. Floating units will directly warm the surface, while submersible de-icers can allow the water temperature to remain more consistent, creating less stress on fish.
When installing a de-icer, it is best to place it as close to the liner as possible at a shallow area of the pond. This will allow the pond to reflect heat more efficiently while the de-icer is running. We also recommend placing the unit away from areas that receive lots of cold airflow. Direct wind can take away more heat than the de-icer produces, possibly causing damage to the unit. If your pond is exposed to a lot of wind, a piece of plywood can also be placed over the de-icer. When using plywood, you will need to make sure that the pond is not entirely covered to allow for adequate airflow.
During operation, you will need to check periodically the de-icer to ensure that it is running properly. If the hole happens to freeze over, it can be thawed out by pouring hot water over the area. Chipping at ice is not recommended, as it causes shockwaves that are harmful to fish.
Although de-icers are normally equipped with a built-in thermostat, they mainly operate based on the water temperature. An air temperature-based thermostat such as the Thermo Cube can be used to have the de-icer only run when necessary, saving on electricity. With adequate preparation and the right equipment, you will be able to provide the best possible environment for fish during the winter.