By late fall, the pond must be thoroughly cleaned to ensure that the water is crystal clear. Debris accumulating at the bottom of the pond must be removed because the intention is to avoid buildup of harmful gases that will remain trapped beneath the ice surface which has nowhere to escape and this will lead to the demise of your goldfish. Try to increase the frequency of water changes and at the same thing avoid wide fluctuations in pH and other water parameters. When the night turns colder, you can even consider using plastic sheeting supported by a solid frame in order to cover the pond surface so that this will help to trap the heat and maintain water temperature to prevent sudden temperature shock causing stress to your goldfish.
When the water temperature starts to approach the freezing level (about few degrees close to about zero Celsius), pond aeration must be immediately stopped so that you don’t risk freezing the whole pond. This will ensure formation of ice only at the surface while your goldfish remains safe underneath it. All the other pond accessories like ultraviolet sterilizer and filters can actually be removed for storage while heater can be left at the pond as a precaution in case you will need to operate it. During the hibernation period, goldfish will start to lose their body weight and their immune system will become weak but there is nothing to worry about because usually they will survive through the winter. As long as the water quality is properly maintained and cleaned before the top surface freezes up, everything should be fine.
At the end of the winter, when temperature starts to rise and the ice begins to melt, immediately follow up with small amount of water changes and give the pond a good cleanup. The quantity of food that you feed to your goldfish should be gradually increased, and during this time, offer some nutritious live foods for them to regain back the lost weight. The beginning of spring is also a good time for goldfish breeding to take place as the natural rise in water temperature will induce spawning.
More about caring for pet goldfish:
» Goldfish health
» Best goldfish care
» Other interesting facts
» Putting goldfish in community tanks