MC wrote:

2) I've read bio filters are useless below 50 degree. So I won't run
it. Is it better to remove it from the pond, or just leave it? I
anticipate the heater will keep my pond around 40. I don't intend on
"heating" it, just keeping it from freezing solid.

40? _That_ is some amount of heat. If an aquarium heater works at all,
your surface temperature is going to be within a degree or two of the
freezing point. Forget the heater, use a bubbler.
--
derek