Frozen food is another good solution, especially when you do not have the live one. Young Flowerhorn usually eat chironomus, brine shrimps and other frozen fish foods, while older ones could not notice them; at their place you can offer frozen fish for human use, you have a great choice, anyway if possible get freshwater fish and avoid the sea ones.
Both live and frozen food can pollute the water, so be sure that Flowerhorn eats all the given food in 5 minutes maximum, in case of rests remove them fast; for this reason it is better to have an aquarium set up that allow you to clean fast without needing to move objects.
Dry standard fish food is a good complementary option, especially if it is of good quality. You can find special foodproduced for cichlids that usually consist of big pellets that Flowerhornlike.
A Flowerhorn cichlid should be fed two times a day, everyday, anyway be careful with the quantities and avoid to overfeed it, reducing the food amount specially if it is really rich of nutrients.
source : http://frogstone-restday.blogspot.com/2009/11/feeding-flowerhorn.html