me too dave, it'd be funny if it werent so sad.
i dont know anything about tilapia or much about mixing thermodynamics but had a couple thoughts.....
first, do tilapia hang in the shallows, the deep, or all over pond?
if adding water of different chemistry and temperature with no circulation or aeration i could imagine you could create a thermocline or stratified body of water. if you add the water to the top you get an upper warm layer through winter. if you add the water from bottom a) you get warmer conditions at bottom and b) you induce more mixing (not necessarily desirable in larger pond) as the warm water wants to rise through the cold.
so if tilapia have a preferred place to hang out, add the well water at the appropriate depth.
ok, blow my theory out of the pond
