As the cooler weather approaches, and your pond water temperature is around 70 degrees, you will want to include feed for your fish that is composed of a wheat germ base or in other words, fish food that has a much lower protein content, with your regular feed. At about 60 degrees, feed just the wheat germ base food. Fish do not digest their food as well when the water becomes colder so don't feed your fish at all after water temps reach 50-55.
In the early fall, you may want to divide and repot your plants. This will allow the cut surfaces and stressed plants time to heal before winter sets in. Don’t forget to tag or label them because come spring you will probably not remember what was what.
Your barley straw probably is pretty decomposed at this point and you may want to add a new bag/bale now to discourage string algae growth during the winter.
Shortly before or right after your first heavy frost, trim back the lilies and marginal plants and discard the plant matter that would freeze and drop into the water. You want very little decaying organic waste lying on the bottom of the pond for the winter because as it rots, it gives off a toxic gas, plus consumes the oxygen your fish will need. Remove the plant stands that held the pots from the pond. You can either vacuum the bottom or scoop out as much crud as possible with a fine net. Put the lily pots back on the bottom of the pond below the point where there is a chance of freezing and return the marginal plants to their original location. If you have tropical plants, you will want to relocate them to a warmer spot for the winter.
To easily access your pots without getting in the pond, use pots which come with handles or install your own handles. If your pots do not have handles, drill two holes exactly opposite each other near the top of the pots. Insert a length of plastic/polyester rope and tie a knot on the inside to hold it in place. You can use a broom handle or a metal pool tool holder to make a pot retriever. Purchase a large hook used to hang bicycles in the garage. Screw the threaded end into the rubber gripper on the metal pole or broom handle or insert the hook into a piece of doweling that will fit into the open end of the metal pole. Run a couple of metal screws through the sides of the pole to hold the dowel in place. You may be able to use your skimmer net handle and make it do double duty.
To avoid a mess of leaves in your pond, you may want to build some sort of cover for it. Another option is to net your pond with bird netting or net that is sold for that purpose. You can use 2' X 4's, PVC pipe, or aluminum pipe/tubes to make a frame and attach the netting to the pipes with plastic clips made for that purpose. Or you can hold the net down around the edges with rocks or stakes, making sure the net is totally above the water so that your fish don't get caught in it. Your "in pond skimmer" will be overwhelmed if you have many trees in your area and your pond is not netted. When the pond surface begins to freeze, remove the net.
You may leave your pump running until you see ice forming on your waterfall, if you have one. Then turn it off to avoid the ice diverting the water flow and emptying your pond. Or if you don't have a waterfall, remove the pump when the water temperature reaches about 40 degrees. If you are using a submersible pump, pull it out of the pond and store it in the basement in a bucket of water. Do not leave a pump running on the bottom of the pond as it moves the water too much and lowers the overall water temp.
Clean your biological filter media and let it dry thoroughly before storing it away to avoid bad smells and the sludge/bacteria drying into it. I have heard of leaving the media lying on the bottom of the pond hoping that some of the bacteria would survive the cold weather but do not know if this works or not. I suspect it doesn't.
If you have an abundance of young fish that have appeared now that their hiding places have been altered, you might want to consider removing them from your pond at this point. It is illegal to release them into your local river or lake in most states. Some ponders have had luck selling their pond babies to local pet stores or exchanging them for store merchandise. You do not want to have excess fishie mutts using up the oxygen during the winter and depriving your old friends of what they need to survive.
You will want to keep a hole in the ice to accomplish oxygen exchange and to make a spot for the toxic gasses to escape. This can be accomplished in several ways. There are many deicers which can be purchased that use very few watts of electricity and up to 1500 watts. You are not trying to heat your pond, just keep a hole open in the ice. Some deicers come with a built in thermostat. Some float and some are just under the surface. A DIY deicer is easily made with inexpensive materials purchased at your local home improvement store. The heat is achieved with a simple light bulb. You can purchase a "thermo" plug for around $10 which will activate your deicer at a certain temperature and turn it off at another.
Some people use an air stone to achieve an "air hole". You should put your air pump in an insulated container outside the pond, because it provides dryer air and is warmer in the box than outside. You'll want to avoid moisture condensation in the tube so that the moisture doesn’t freeze and block the air from achieving it’s purpose. Do not stir up the sludge by installing your airstone on the bottom of the pond.
Should the ice form before you have installed your method of keeping an opening, you need to make a hole. Do not forcibly strike the ice surface. Lay a pan of hot water on it until a hole forms. The flame from a blow torch works well also.
When using or working around electricity and water, always have your Ground Fault Interrupter installed and working.
If you choose to use a Skippy or purchased biological filter to feed your waterfall, you should clean it when the pump is shut down. You can let the water gravity back to your pond veeeeery slowly, and then remove the sludge by scooping it out. If you have a clean out valve, open it while there is water in the container to release the built up sludge in the bottom. Of course you can siphon/suction the crud off the bottom.
Make sure any surface pipes that can hold water and freeze are emptied either by gravity or blowing them out by reversing the airflow of your shop vac.
Bid your fishies good night and tell them you’ll see them in the spring.