Have you tried feeding black worms? I have some bangii cardinals that just picked up at my local fish store and they will only eat live food. I have been feeding black worms (their fresh water and die quickly in a saltwater tank) and when I drop some in the tank they are gone in a couple of seconds. I'm hoping to get the cardnals to sometime eat flaked or pellet food. I would try to help you nurse him/her back to health in my 125, however, I have grown attached to my coco worm and I think the melanurus would make a meal of my coco worm.