hammer or a big rock to hit his head.. jk
1.Water quality is a VITAL
2.High quality fish staple pellet for chiclid.. not for goldfish etc.. they will eat anything.. but there's a different diet for carnivorous and herbivorous..
e.g Hikari chiclid staple,gold,bio-gold+,Hikari jumbostick,grand sumo,New life spectrum(NLS),tetra color chiclid,Sera flowerhorn,ocean free xo humphead,starry,sysred etc
there's many theory bout feeding anyway.. there's people like to garlic+multivitamin+ocean free "fish beautifier"+any pellet --' the conclusion is just give a suit diet with lots vitamin for your flowerhorn requirement..
3.Shrimp/krill/salmon meat occasionally(I know it is for color since shrimp/krill contain astaxanthin but still it is good source of natural protein also)
there's many thing you may find information from internet..
somehow..as I practical with this kind of fish more than 15yrs..there's a lot of theory like do nuchal hump exercise by using mirror to make them angry(stress) or give another flowerhorn next to another(using clear glass as divider)to make his kok grow(dominant fish article)but for me..it is cause of genetic and water quality(water quality is a key to success in fish hobbies)but still you can make your flowerhorn to reach his optimum potential if you did a good care with your flowerhorn..
I got three 3'' zz flowerhorn and daily I just give them not really too special food "chiclid gold and staple'' and I do keep 25% water changes weekly.. I do like the way their nuchal hump.. it's like I just see an adult grown flowerhorn with a round nuchal hump..
conclusion
*check water quality with sufficient supplement from food and make them energetic recognize(like a puppy wagging his tail) you as a owner is much better profilic than a big kok but not even recognize you as the owner hehehe.. peace