Starve him...bump up the temperature to 83-86 degrees. Let him starve for 2 days and 2 nights. Try it afterward, if it won't eat still. Feed him what he eats and starve him again, but this time make it 3 days and 3 nights. It should start making eat...never give a flowerhorn on how they want. Treat them as a dog, a stubborn flowerhorn is no good.