"Madd Hatter" wrote:

I was wondering if anyone has any ideas on making a heater for a 700-750
gallon in ground pond, to keep it at about 75 deg in the summer months? I am
in the Toronto area, and from what i've gathered so far, I shouldbe looking
at 65 to 69 degrees low during the summer here. I want to make it as stable
as possible.

You need a heater of some kind, and an electronic control to regulate
it.

Heaters are simple resistive electronic circuits, so you could look for
a proportional heater control circuit.

A really honking big aquarium heater or two may do it as well. I'm
thinking more about the in-line pipe heaters than in-tank ones.