In winterizing your pond the first and most important step in winterizing a pond is to determine if the depth of the water is sufficient to support your fish in the winter. A good rule of thumb is to look first at the zone in which you live.
For zones 4-6, a depth of 3 to 4 feet in part of the pond is sufficient. You can check with a local pet store to determine the zone. If you so desire, after deciding to winter your fish you may add a heater with a thermostat to keep a portion of your pond above freezing.
For a garden ponds depth below the 3-foot mark you will need to insulate the pond with straw, plywood, foam taking care not to cover the surface completely. There must be an air exchange via a hole in the ice to keep noxious gases from building up in the pond, killing your fish.
Beginning in September, add fish vitamins to the fish food, bring in the plants, with water basins beneath them, placing them in a sunny location.
Use a pond heater once the water temperature drops below 52 degrees Fahrenheit or 10 degrees Celsius and discontinue feeding. Your fish are now dormant until spring.
Remove your pump, store indoors, empty hoses, clean debris from the pond. Once the pond begins to freeze, gently create a hole by setting a pan of hot water on the surface to melt a hole. Do not tap or try to break the ice because the sudden shock could kill your fish.
Essentially what you are doing here is just bringing in plants and pond pump, emptying the hoses of excess water, and removing debris. Drain the pond down to about 1/4 of its capacity. This will weigh the liner down and allow the frozen water to expand while not damaging your pond liner.
Cover the pond with netting or a pond cover to keep snow, ice and critters out. Floating a few pieces of firewood on top will help maintain shape.
In spring, if you keep fish and have brought them in for the winter, re-introduce them to the pond by placing one or two of the fish into a bag, that has been filled with water they have been in already, into your pond. By placing the entire bag into the pond, the fish will adapt to the new environment after about 20-30 minutes, at which time you can release them into your pond.
If you have the room to store your pump in a warm place, by all means, remove the pump and bring it indoors.Most pumps can be stored dry, but a few of the more complex models may need deionized or distilled water poured into the chamber(s). Very little other maintenance of the pump is necessary because most of today's pumps are sealed units.
If you keep the pump in the pond, move it closer to the surface, just under the ice, and use pond de-icer close to the intake valve. For zones 4-6, it may not be prudent to leave the pump in the pond if the total capacity of your pond is less than 500 gallons.
In short, if you follow these steps to winterizing your pond, it will give you many years of enjoyment.