Minnows = BAD. Stop feeding them. They contain Thiamnaise (B1 definciancy).

I would stop feeding him minnows for like a week or 2, and continue scenting the pinky (it's gotta be pinkies btw) with the minnows and offering that. Just rub the minnow on the pinky and feed it. The hunger (from my feeding the fish) should make him much more open to the pinky. Always works for me