Hi--have had a little experience in using well water to top off ponds and do 10
to 30% water changes, but in much more extreame conditions (zone 5 MI). The
temperature differences you are talking about are really quite minor for just
"topping off". The air temp swings of over 50F in this area with fairly wide
water temp swings in the same 24 hours rarely have much effect on the pond
other than to slow it down so feeding and the like need to be slowed too. As
far as the water stratification is concerned--not in 2 feet of water. Takes
much deeper water in calm circumstances to do that.