Water Gardening: Need help for wintering koi!, 1 by DRH2

DRH2 wrote:
Hi Liz,
A couple of comments regarding the temperature and temperature swings. You'll see a chart below that shows what types of temperatures I see here in zone 4 (I apologize for the size of the file but it's necessary to get the chart resolution). The larger the volume of your pond the more the water temperature swings will be reduced or dampened compared to the air temperature. I've recorded the air temperature as well as the surface water, mid-depth and at the bottom of my pond (approx. 3000 gallons - 3 feet deep). So for your 50 gallon pond you may find that the temperatures will vary nearly as widely as the air temp. However, your fish should be able to survive those temperature swings since it's doubtful that even in your zone that you'll get a temperature drop say on the order of 15°F in 10 minutes! Even that would probably be dampened out by your 50 gallons.

There was a recent article regarding temperature and temperature fluctuations in a national Water Gardening magazine written by a veterinarian. Some of his suggestions were okay but one in particular I’m not sure I would use: putting a plastic insulation blanket (similar to ones used on swimming pools) on the pond at night to reduce drops in temperature. This would significantly reduce gas exchange as well as availability of oxygen.

While I don’t particularly care for heaters you could, in this instance, use the smallest livestock water heater you can find (the types sold in Farm & Feed stores used for keeping water troughs open during the winter). You would want to look for one that has a built in, automatic temperature shut off. If the capacity is too high (it is supplying more watts than you really need) you can run it through a device commonly called a “variac” and adjust the power supplied to the unit. Alternatively, if you know someone or if you are comfortable with a bit of wiring there are temperature monitors with built-in set points/shut-offs that you could also use to control the heater.

Come spring, yep, you’re going to want a bigger pond!! :-))

As to feeding the fish - I’d go with what has been mentioned above. I generally stop feeding when I know the water temperature is going to be consistently below 50° F. How do you know that it will remain that way? I usually check out the 7 day forecast to get an idea of where it’s headed. Of course up here our temperatures tend to head “South” in a short period of time! :-))