It’s another beautiful fall in Colorado. For those of us that enjoy fish ponds, this is a time of shutting down all those things that can succumb to those cold wintery nights. We have enjoyed the lazy days sitting next to our ponds, but now it is time to decide whether to bring the fish inside or prepare the pond so that it doesn’t freeze. There are advantages to both: moving operations indoors promotes a never ending growing season with feeding throughout the year, but also maintenance throughout the year of the fish. Also it requires an indoor pond or aquarium with heating and filtration. Then of course is the challenge of moving the fish into that indoor situation, which may have some thermal consequences. On the other side, those that want to keep their fish outdoors need to consider how to avoid freezing the pond. Logistically this means some kind of heater or de-icer. It is also a good time to be sure that minimal organics are in the water. Chemicals and feeding usually are not necessary when the temperatures drop much below 40 degrees at night.
As temperature in the water drops, things change not only in the fish but also in their environment and needs. Most Koi tolerate cool water temperatures and actually have more problems with rapidly changing temperatures and big temperature swings. Water features, such as water falls and fountains can be shut down for the season. Running these features can chill the water, and in some cases, supercool the water (Temperatures of the water actually drop below freezing). Chemicals such as salt can also supercool the water so typically it is not recommended to add chemicals to the water.
Bacterial, parasitic and protozoan numbers drop dramatically, so disease processes that have a living agent involved (besides the fish) become less of a concern. Correspondingly the immune system of the fish also starts shutting down. This becomes a problem if the temperatures in the winter become very warm suddenly allowing pathogens to propagate, with the fishes immune system not getting to adjust. Ozonators and UV light systems can be taken out of the filtration line. Of course this assumes that the fish are healthy going into the winter.
The main issue that we have then with temperature relates to preventing the pond from freezing over. De-icers for large animal troughs, aquarium heaters, etc. can be used to keep the pond from freezing over. Of course, do not expect an aquarium heater to keep a 10,000 gallon pond free of ice. A number of de-icers may be needed. It is not the volume of water to be kept ice free that is important, but the surface area of the pond. Should the pond be greater than 4 feet deep and insulated with ground or some other form of protective side, the surface of the pond could freeze without the fish being in immediate danger. In these cases, keeping an air hole in the ice is necessary, but the pond likely will not completely freeze.
Typically since our fish become less active when the temperature drops their need for nutrients decreases. (Most koi fanciers will stop feeding when the temperatures of the water drops below 50 degrees.) They are producing less waste product and hence less organic matter in the water. The biggest problem we see at this time of year lies in the leaves that fall into the ponds providing a significant organic bed at the bottom of the pond. This can also clog filtration systems. In general, the quicker leaves are removed the less it becomes an issue. Some plant chemicals, especially if the trees have been treated in the fall may provide toxic substances into the system.. Most pond owners take this time to clean out the ponds of as much organic material as possible before the Spring warm up occurs.
Should the koi owner decide to bring the koi inside, then the issues of maintaining an aquarium return – maintaining water quality, feeding, avoiding / dealing with moving the koi and the stress associated therewith, quarantine procedures, water changes, etc. In many cases, this is more daunting a process than keeping tropical fish, even though indoor temperatures are ok for the koi (no heat necessary.)
If you have any specific questions please feel free to call me at 303-469-7387. Enjoy those “dog days” or perhaps we should call them “koi days” of summer.