i have been keeping the regal angel for 5 years now.. i started out with giving them real tiger shrimp cut in small pieces.. and Mussels and squid pack from Asian market.
just leave in the corner and see if he/she eats it. now my angel fish eats off my finger tips.. brine shrimp, pallet, marine fish formula, Nori.. ..
good luck .. he/she needs to eat something to gain some weight.