I believe I remember reading in PB that one has to be careful feeding in the northern US so as not to have too productive of a pond. The more productive the higher chance for problems. For that reason I thought there might be some relative cut off for feeding.
Had a winter kill 6 years ago, but that was before I had it cleaned out and enlarged, now 1/3 is 11' and 2/3 5'. I put in an Air 1+ this spring. I am at about 1500' and in a snow belt, so some of the winters can be pretty harsh.
I don't need to have the largest fish in the north, but like to feed to help growth rates. Ted