It is a misconception that running water during the winter months somehow hurts your fish. After all they are cold blooded creatures and adapt to whatever the water temperature is at any given time. Secondly running water freezes slower than still water. Therefore with some precautions you can continue to run your waterfall well into winter. Mainly you just have to be sure that the waterfall or filter outlet flow does not freeze to the point that water gets diverted out of the pond therefore draining it.
Help them in early Fall to survive by doing the following: Add a vitamin and mineral supplement to their diet to help them build up their immune systems and add the needed stored fat to get through the hibernation cycle. Once the water temperature drops to 55 or lower only feed them when they are actively up and roaming around. If they are hanging around at the bottom do not feed. Only feed them what they will eat in a few minutes and remove as much of the uneaten food as possible. When the water temperature is below 45 do not feed at all, even on warm days where the nighttime water temperature will return to 45 or less. Ammonia is the number one fish killer. During the winter your fish will not die from the cold they actually might suffocate due to the water becoming toxic. Ammonia builds up at the bottom of the pond, the very place your fish want to spend the winter, while carbon dioxide builds up near the surface under the ice. A pond deicer (heater) may helps some with the carbon dioxide problem, but does nothing to prevent ammonia build up. Ammonia forms because of several reasons. It is part of the natural biological process, when organic matter is in the pond, dead plant life, fish waste etc., ammonia is the first thing given off during the decaying process. The bodily functions of the fish also greatly contribute to ammonia in the pond. Yes their waste is part of it, but actually some 70% or more is coming from their gill function. As they breathe they give off ammonia and carbon dioxide. During their winter hibernation their whole system slows down, but they still breathe and produce waste matter. It is very important to allow dissolved oxygen into the pond and do something to prevent the ammonia and carbon dioxide build up. A deicer (heater) just does not do the best job possible. The answer is an Aerator/Circulator Decontaminator Unit. Using one of these units and a deicer as a back up is the best solution. Use the Aerator/Circulator Decontaminator all year round as it greatly enhances the overall biological process helping to prevent algae and such, but it is very important in the winter and should be added to the pond in early Fall to provide a clean, clear and healthy environment for your fish. The explosion of bubbles will constantly add dissolved oxygen to the depths of the pond, while helping to keep a hole open in the ice. Even if your pond froze completely over the unit would continue to work bringing a fresh supply of oxygen, while absorbing toxicants. Again a deicer (heater) will only add a little surface oxygen and does nothing to prevent ammonia.
Tropical plants are not going to make it through the winter, if left in the pond (if you live where you have a 'real' winter). They should be removed as soon as the water temperature drops below 60. Depending on the variety use them as house plants. Water hyacinth and lettuce take a lot of work and money to keep alive all winter so it is best to consider them annuals and just replace each spring. Your hardy plants need to be cut down to about an inch above the root stem and sink them a little deeper if you like. However, remember your fish, they need a place to hibernate so give the fish the top priority as far as room is concerned. Best time to cut the hardy plants back is long before there is a chance of frost. While removing the hardy plants to cut them back remove any debris and string algae from the pots and stems.
In you have an out of the pond biological filter, you can let it continue to run until there is the chance that the outlet water flow might freeze to the point that water could get diverted from the pond. If you shut it down let the water drain from it either via siphon effect or from the drain plug. Do not clean it other than to remove any dead plant life, leaves etc. An in the pond filter should be removed for winter. Check your pump manufacturer's instructions (yup -- you should have kept them). Remove as much debris as you can from the pond. Net out dead plant material, leaves, waste, sludge etc., but do not over do it. Try not to murk up the water too much. During the winter, check on your pond often to make sure all is going well. If the pond has completely frozen over NEVER break it, by pounding on it etc. Sometimes during the very coldest of winters the recommended Aerator/Circulator Decontaminator may not keep a hole open in the ice all the time. Do not panic, remember the unit is still working bringing in oxygen and absorbing toxicants. If this happens, now is the time to plug in the deicer, but just until the ice opens. Another thing to do is pour hot water until the hole opens again.
COME BACK SOON