You should always always always ask them to feed it in front of you. Seems kinda rude I know but it really is the best thing to do. I always ask them and they do.
180g Reef - 60g Rimless Reef -90G FOWLR- 125g Malawi Cichlids- 40b REEF- 34g Fresh Planted-working on- 20L FOWLR- working on
I have a mix of many different saltwater fish amongst my tanks, but I love my Tangs most of all.