Gan, you have been at my place and you know I have a well underneath my fish room and bare in mind that my fishroom is outside
in the yard. Yes the temperature of the water in the well is about 2/3 deg less then that in the aquariums. I cannot do any better
but due to the fact that the new water from the well whilst donig a water change is poured slowly in the aquariums , the change
in temp does not effect the fish that much. I switch on the gas heater round about 9pm and switch it off round about 7.00am
( depending on the outside temperature of course ) During the day the temp of the aquariums drops with approx 2/3 deg. I have
been using this method for about 6 years now without any adverse effects.