flowerhorn aren't made to eat fish.. only one or two of the parent species are anything other than opportunistic piscivores. And viejas like synspilum (source of the red in ZZRD) and others used in kamfa, are almost exclusive vegetarians in the wild. Most of the species animal diet consists mainly of things like insects and crustaceons.. thank things like worms, crickets, mealworms etc.. or like oddball said... "ghost shrimp, scuds, earthworms, snails, dwarf crayfish, maggots, etc."
Allthough they often do not like the taste of algae pellets, it is also important Imo to have some vegetable in the diet of any amph or vieja fh.. I use goldfish food for this as it is often fortified with more vegetable matter
shrimp arent a good option imo cuz they tend to eat the gravel while catching them,, unless u have sand or a bare bottom tank this can potentailly lead to injury with boisterous feeders.