I wouldn't feed my flowerhorn how much it wants. I have stingrays as well and they can eat everything I put at them.
Feed them as much as they can eat within a 2 minute span. If there is leftover take them out it will just cause unnecessary waste.
I feed new spectrum light, Shrimp pellets and Hikari gold plus. Occoasial blood worms and brine shrimp. I feed my fish everyday. Sometimes I skip a feeding as well on purpose.
I feed a variety of pellets to my cichlids, and they show good color. The main two are Hikari gold and NLS. I'm assuming this diet will also work with Flowerhorns, since they are cichlids, and since Ihsnshaik had success with it.