Posted: Tue Dec 02, 2008 8:33 pm
If your turts aren't hatchlings and they're healthy, that's not a bad temp range for them (my RES lives in water that's pretty much around 70F in the winter). Having the temp constant would be good, especially in the winter, though. (How is the water staying that warm without a heater in Montana in December?)
For a heater, allow 3-5 watts per gallon of water. If you do have 100 gallons in the pond, using 5 watts per gallon, you'd need about 500 watts of heater. Since the pond is 7', rather than just one heater, I'd have two 250-watt heaters, with one positioned near the filter output and one on the opposite side of the pond.
"You become responsible, forever, for what you have tamed." -Antoine de Saint Exupery-