Remove any fallen leaves or excess plant matter from the pond. Before the leaves begin to fall, cover your pond with pond netting. This will help keep unwanted leaves out. It is much easier to keep leaves out than to remove them after they fall into the pond. Otherwise, skim your pond at least once a week, using a fine net or pond vacuum. Leaves or plant matter left in the pond over the winter will deteriorate and produce organic waste. However, a patch of leaves left in the deepest part of the pond can help to provide shelter for over-wintering fish.

Perform a 20% to 30% water change. Doing a water change, one month or so before the anticipated "closing of the pond", helps to remove excess organic matter. Top up your pond with fresh water, not forgetting to condition the new water during refill.

Disconnect your UV sterilizer. If you use a UV sterilizer, you should disconnect it around the same time you stop feeding your fish. As the temperature of the pond drops, bacterial growth inside your pond and biological filter slows down, as does algae. As UV sterilizers kill off beneficial bacteria as well as algae, it is important to conserve as much bacteria at this time as possible. Clean and store your UV sterilizer in a cool dry place.

Clean out your external filters. Remove the filter mats and bags of biological media from your biological filter. Rinse them down and store them in a dry spot. If left over the winter, all filtration media may freeze into a solid block, making spring clean out harder then necessary.

Prepare your plants and fish for over wintering.Read on for more suggestions as to how to prepare for plants and fish for winter outside.

Determine which winter oxygenating method works best for you and your pond. The four most trusted methods are listed below. Continue reading to find the one that works for you.

Remove and discard any floating plants (lettuce and hyacinths) as well as any tropical oxygenators. Cut back hardy marginal plants. Once hardy plants have begun to die back, cut the stems to within 1" of the soil line. Drop them to the deepest section of the pond. If you decide to leave them on the plant shelf, do not cut back your hardy aquatic plants until the spring. If you are limited on space, you can bring your plants inside. Put them in boxes (or plastic tubs) lined with trash bags, and place them in a cool, dark location inside. Keep them damp (remember to check on them occasionally).

Remove tropicals plants from the pond, and bring them inside. Tropical pond plants will not survive the cold, and if left in the pond will not survive the cold, and if left in the pond will decay and pollute the water. This also applies to tropical water lilies.

Trim back hardy water lilies. Cut dead leaves off hardy water lilies, and drop the plant to the deepest part of the pond. In order to successfully over-winter, hardy water lilies need to be in at least 2 feet of water. Hardy water lotus does better under at least 3 feet of water. Unlike hardy lilies, lotus leaves should not be trimmed back.

During the autumn months, feed your fish a high quality, highly digestible food. As the water temperature of your pond begins to fall, your fish will require less food. Watch their rate of consumption closely, and adjust your feeding. Once the water temperature of your pond reaches 45˚F, stop feeding your fish completely. At this temperature, fish will hibernate at the bottom of the pond. Fish will occasionally come to the surface of the pond during the winter. Still do not feed them. They are surfacing for oxygen not food. Similarly, do not feed them if the outside temperature rises. Only begin feeding your fish again once the average temperature of your pond water is above 45˚F. Over wintering fish need a section of water at least 2 feet in depth, as well as a hole in the ice for gas exchange.

During the winter, it is important to keep an opening in the ice, especially if you are over-wintering fish in your pond. The importance of this is two-fold. First, while your fish are hibernating their way through winter, they are still producing waste. This waste, along with decay plant debris, produces gases that can be toxic to your fish. Second, oxygenated water is vital to your fishes’ survival

through the winter, despite their slumbering state. Keeping a hole in the ice prevents the buildup of toxic gases, as well as allows for continued oxygenation. Any of the following four options will achieve both these goals.

A pump that circulates the water at least 2000 gallons/hour is enough to keep an opening in the ice, as well as oxygenate the water. Special consideration should be noted for long or slow-moving streams as well as areas around the waterfall. In such areas, it’s easy for ice dams to form, causing the water to be diverted over the liner. It’s important to watch for this, especially on very cold day. If you find that this is the case in your pond, it is best to turn off the pump, and use another oxygenating method. For ponds with shorter streams and waterfalls, there is another consideration you’ll need to keep in mind. Even during the winter, water from your pond will continue to evaporate or be used up in ice formation. Therefore, you may need in top off your pond so that your pump continues to function properly. Making this extra effort to keep your falls running throughout the winter will produce beautiful ice formations around the falls and streambeds.

If you choose to shut down your pond for the winter, you’ll need to replicate the effects of the waterfall in order keep the water oxygenated, and an opening in the ice. Using a small submergible pump below, but close to, the water’s surface, will achieve the same result. The pump must circulate at least 150 gallons/hour. Allowing the pump to bubble about one inch above the surface will agitate the water enough to keep a hole in the ice. The bubbling effect will keep the water from freezing around the pump. Do not circulate the warmer water from the bottom of the pond with the colder from the top. The ideal location for the pump is about the halfway point of maximum depth.

Option 3: Aeration Stone

Installing an air stone with an indoor/outdoor air pump acts the same as using a small submergible pump. Hang the air stone off one end of the pond just under the water level and let it bubble. The air pump and cords will need to be protected from the elements, either by placing them under an over-turned pot or by running them from inside a shed or garage. The bubble effect of the air-stone will keep an opening in the ice, as well as provide oxygen to the water. At temperatures below 10˚F, a thin layer of slushy ice may form, but should not be solid enough to prevent gas exchange.

Option 4: Pond Heater

Using a floating pond heater is one of the more common methods to maintaining an opening in your ice. However, a floating heater alone will not oxygenate the water, and therefore can be deadly to your fish. Pond heaters are better used in conjunction with an air pump or submergible pump. Likewise, a floating heater can be used when keeping your waterfall running. By placing the heater in front of the pond skimmer, it will prevent ice from blocking the flow of water to the pump.

Using a floating pond heater is one of the more common methods to maintaining an opening in your ice. However, a floating heater alone will not oxygenate the water, and therefore can be deadly to your fish. Pond heaters are better used in conjunction with an air pump or submergible pump. Likewise, a floating heater can be used when keeping your waterfall running. By placing the heater in front of the pond skimmer, it will prevent ice from blocking the flow of water to the pump.