Fish ponds often do not require a large amount of care. But because they are outdoor fixtures, ponds can be a little more difficult to tend to when winter comes. Special considerations are needed to care for ponds and fish through cold-weather months.
Prepare for the winter by feeding your fish with a fish food that is high in protein. This helps them build up their fat reserve so that they need less during the winter months. When winter hits, a fish's metabolism will slow down as the temperature drops, so the more protein in their system, the better chance they will have of surviving the winter.
Stop feeding the fish altogether after the temperature of the water drops below 10 degrees Celsius. When the water gets to be a certain temperature, fish will stop eating entirely. Unconsumed food will mould and create a toxic environment in the pond.
Melt a small hole in any ice that may cover the pond. When the fish produce excrement, their wastes cause toxins to build up in the water that can only escape through the air during evaporation. If ice covers the entire surface of the pond, these toxins will have nowhere to go --- which can kill your fish. Take care not to crack the ice; use hot water or a heating device to slowly melt the ice. Breaking the ice can cause a shock-wave which can possibly kill the fish. However, it is important to note that if you pond is not at least 7-feet deep, the fish should be removed entirely from the pond and housed elsewhere or they will freeze and die.
Prepare the plant life of your pond for the winter. Remove all dead or dying foliage from around the pond and move the remainder of the pond plants deep enough in the water to avoid having their roots frozen. You can purchase a floater heating device from a home and garden store to prevent a small area of the pond from freezing. If you have one of these, place all of your plants near it to prevent them from dying.
Remove all tropical plants from the pond entirely and move them to a temperature-controlled area. This includes plants that cannot be submerged in the water. For these plants, just placing them in your home or a small greenhouse will keep them nicely for the winter. Any plant that begins to die when the temperatures reach below 10 degrees C should be removed.