John this totally sucks. I feel your frustration. Unfortunately is part & parcel with the hobby. I think it might just come down to this being a young system. Balance is a hard thing to achieve and it's an evolving challenge with a new tank.
You have a great fish stock. Give some away if you want but keep the ones you really like (like leopards, especially if they're pellet trained) and take these guys up on a QT tank. I have my fish in a trash can right now...you'd be surprised how easy it can be...I was. Hang in there and don't quit...this will just be a blip, trust me.