The Garden Pond in Winter
In cold weather the fishes need less oxygen and food, and they rest in a state of torpor gradually using up the food stored as layers of fat. When the pond freezes over it keeps oxygen from reaching the water and prevents the toxic gases from leaving it. For the most part the cold is only sufficient for the pond to be frozen over for a few hours, and this is not a hazard to the pond inhabitants. Only when it is covered with ice for a number of days does trouble start to build up.
A pond heater is an ideal answer; drop it into the water, where its float will bring it to the surface. The little power that it uses – the equivalent of an electric-light bulb – will be sufficient to keep an area of water free from ice. Switch it on only when frost is forecast, and keep it on in times of prolonged freezing. An alternative is to fill a can with boiling water and rest it on the ice, which will soon melt. Remove some of the water from under the ice, to leave a gap for air to get in and for the gases to get out.
Remove and clean pumps, then store them for the winter should the makers advise it. If a pump is left in the pond it is important to run it for a few minutes every week or so, to keep the machine parts free and working well.
Pond lights should also be removed and cleaned; remove algae from the glass, check the wiring, and store the lights for the whole winter period.