Can you post a picture? I would like to see his stomach. Feed your flowerhorn as much as you feel is necessary. If food particles come out of his gills, he is definitely getting to much. Also, DO NOT feed your flowerhorn what it can each in 1 or two minutes. I'm not trying to bash on you coflowerhornguy, because each fish is unique. If I fed my fish what he could eat in 1 or 2 min her would eat 100 pellets a feeding. He eats about 20 pellets in 8 seconds. He is a brat and acts like he doesn't ever get to eat!
If you can snap a photo of him it may be easier for us to see his bloat.