How much flow through are you looking at? I would be worried about well water temps being too cool to get good growth rates. I am currently feed training a bunch of little RES in a 75 gallon tank and using an aquarium heater to keep the water temp right at 78 degrees. I am doing a 10% water change daily while cleaning the bottom of the tank as well as aerating and running a couple of large sponge filters. My little RES are eating well and getting fat. My daily water change typically knocks the water temp down 3 or 4 degress but comes right back up with the aquarium heater. IMO good growth rates will depend on optimal water temps in the tank and keeping nitrite levels in check.