Once they start eating they'll generally take most types of food sold at your LFS, flake, mysis, brine shrimp, CycloPeeze granules. My first Maroon didn't eat for an entire week and I was quite worried. He swam back & forth along the glass the whole time, no idea where the energy came from to do that so long without eating. Out of the blue he started eating most anything. He is now a large She with a little mate. The male is more finicky and seems to eat only brine shrimp and CycloPeeze granules.
I added my GBTA about 3 months after introducing the first clownfish and it took a week or so for him to host. I may have added the BTA a little sooner than is advisable, but it survives to this day. Give yourself at least 4 to 5 months with your tank before adding the nem. Less chance of a mishap that way.