If you want a clear and healthy pond in spring some proper procedures for a shut down should be followed.
Closing your pond properly, for the winter months, is one of the best things you can do for the next pond season. Obviously these procedures do not apply to everyone in the nation, but they do apply to most.
Marginal plants are generally clipped 2" above the water line. You may want to winterize these plants last, in case the weather suddenly warms and causes them to grow. This will eliminate the need to cut them again.
Surface plants should to be removed and discarded. Most are tropical in nature and will not make it through the winter months. Submerged or oxygenating plants can survive under certain conditions. Usually the deeper your pond the more likely they will survive.
Lastly, remove foliage and debris thoroughly from the plants. Leaving this debris in your pond will foul it and create more work for you in the spring.
About The Fish:
One thing you can do for them prior to the cold weather, is give them a clean environment in which to live. Also placing 2' sections of 4" PVC pipe will give them a place to winter over. Drill a hole in each end and tie a short piece of fishing line with heavy weight to the pipe. This will keep it on the bottom and in place. You may also want to use a product that will place a slime coating back on the fish. Using pond salt will also help. I recommend our Heals-All, which contains a double slime coat as well as Vitamin B-12 to heal any wounds or cuts the fish may have in preparation for winter.
If you live in an area where the pond will be covered over by ice, then it may be necessary to install a pond de-icer. See Equipment section below.
Chemicals And Treatments:
Covering Your Pond:
The most obvious way to cover your pond is with nylon pond netting. This netting is strong and will not rot or decay, making it the choice of pond owners everywhere. This netting is extremely important in keeping out the leaves and trash the eventually ends up in everyone's yard. The netting is stretched tightly across the pond and anchored with plastic stakes or rock. One good idea is to place a floating object in the pond to make the netting take on a tent like appearance instead of eventually ending up lying in the water. You can also use foam, beach balls, even the blow up rubber toys used in pools. Either way, get the netting raised up above the surface.
Many products are on the market that will keep an open hole in a frozen pond. Without this hole allowing trapped gases to escape, fish will suffocate and die. The best defense is a simple thermostatically controlled pond deicer that comes on at a certain temp and off at a certain temp, protecting your investment.
Disconnect and clean all of the equipment in your pond. This means the pump, filter systems and UV sterilizers. Let them air dry prior to storing in your shed or garage. To properly clean a UV, mix a solution of 50/50 water and Clorox 2, NOT REGULAR CLOROX. Place masking tape over one of the holes. Pour solution into the UV until it is about half full. Place tape or your hand over the other end and shake vigorously for 2 minutes. Pour out and repeat. Next, remove the tape and lay the UV on the ground. Place the end of your garden hose in one end and turn on at about 50%. Let the water run through it for at least 5 minutes. Now turn the UV 180 degrees and repeat the procedure. This way the UV will be properly rinsed and will not harm fish or plants in the spring.
(excerpted from an article at Patio Garden Ponds in Oklahoma City)