I have a copperband butterfly, a blue stripe pipefish, and a leopard wrasse.
The CBB butterfly is by far the pickiest. He will only eat LRS reef frenzy but he eats a ton of it. I usually hand feed it to him so I make sure he gets enough. I made sure to see him eat in the store though so he basically ate in my tank right away once I figured out he only wanted LRS. I’ve had him for about 6 months.
The leopard wrasse will eat anything I add to the tank. Right now, she eats frozen, pellets, and some live when I supplement with hatched baby brine. Again, I made sure to see her eat in the store before buying her. I’ve had her for about 9 months.
The blue stripe pipefish eats frozen. Even with his small mouth, he can eat pieces of mysis but definitely prefers smaller foods. I’m pretty sure he hunts in the rocks all day because I really only see him when I’m feeding. He also likes live baby brine shrimp. He’s in a mixed reef but is a great swimmer. He came in the tank I bought and has been in captivity for around 2 years now.
In my experience, only buying healthy fish that eat in the store is a key. I did buy one leopard back when I didn’t know what I was doing with a pinched head/neck. Although she was an aggressive eater, she didn’t make it.