Pumps, filters and UV lights
When temperatures drop, winter pond care is necessary. Algae growth stop, so you can disconnect your filter and UV light if you have one. Remember you only need filters and UV lights if you feed fish. If you make them work for their room and board by eating submerged vegetation and in turn fertilizing it, you have no need for filtration or UV lights.
As the temperatures drop to 39 degrees F, turn off all pumps and fountains. Fish like to stay in the bottom of the pond where the water is warmer, so don't stir up the water and lose the bottom layer of warmer water.
Remove your pumps now, check the hoses for leaks. Clean your pump, clean and wipe down your filters and UV lights. To clean tubes and remove lime scale, you can wipe them with vinegar.
When the pond freezes over, you must create an ice free opening in the ice, so gases can be exchanged and the fish can breathe. You can buy deicers, but if you do, buy the ones that are used to keep horse trough water from freezing. They cost about 1/4th as much and work better. And cost much less to run. Another way to keep a hole open is with a plastic jug that milk or water came in. Put a couple of cups of water in the jug, tie a string on it and float it in the water, tying the string to something you can reach easily. If the pond stays iced over in the morning, pull the jug out and you will have a hole in the ice. If the temperatures stay below freezing all day and you expect them to stay there, you must use several jugs or a different method altogether. You must be vigilant if the temperatures continue below freezing because ammonia and carbon dioxide build up from fish breathing. Ammonia is also generated from decomposing plant material and fish waste. If these gases can't escape, your fish can die, plus they need oxygen to breathe.
If your pond does freeze over completely for more than a day, do NOT whack it with a hammer to open it. The shock can kill your fish. Use warm, not hot, water from your inside faucet to open a hole. Just run it over the ice or put it in a pot or bucket and put it on the ice. You can also run water from your garden hose and the ice will melt, unless you live where the hose is frozen too. I have heard of people putting a piece of black visqueen on the ice to thaw it, but have never tried it. Let me know if it works. You can do these things daily, but I think the plastic jug is easier. And, of course, the deicer is easiest, but also costs a few dollars.
Some people build a frame over their pond, like a cold frame, out of PVC and visqueen to keep the pond warmer and protect it from debris falling in the winter. This can be a good idea because we tend not to pay as much attention to the pond in winter and a small problem can become a disaster if not prevented.
Do not run a pump that brings the warmer water up from the bottom of the pond to the top. Pretty soon all the water will be cold. If you do put a pump in the water, raise it to only 10 or so inches from the top. That will leave the warm water at the bottom where the fish are more comfortable.
Fish food, liquid bacteria, fertilizers
Now is the time to discard all fish food, if you have been feeding fish. It loses nutrients over time, so throw it away and buy new in the spring.
Buy all the pond things now that you might need this winter because no stores stock pond supplies in the winter.
Be sure you have enough dechlor, Microbe-Lift and any fish meds you may need.
If you do these few simple tasks, your pond will come alive happy and healthy next spring.