Surely wrapping 50ft of hose in the sump does the same thing.....I.e. why does the water in the pipe reach the same as the tank....cos the heat transfer from sump to pipe...therefore it is the same energy loss. I agree the water entering at the end of the pipe will probably be matched to the sump temp but it takes the heat from the sump....it's a basic radiator.
The other thing is oxygen depletion, if you want to build something anearobic you run it slowly through 50 ft of pipe.
Just my ramblings!
