Suggestions for a 55

[Eyford01]

Alrighty then, I have a 55g mixed reef with attached 29g sump/fuge current residents include CUC snails and crabs, sps lps and softies, 1 neon goby 1 hectors goby 1 firefish 1 yellow watchman and 2 mandarin (soon to be 1 as soon as I can net one)
so I was thinking a yellow tang maybe? I looked into tangs at one point and decided the tank was too small but am now revisiting the idea, does anyone know of a smaller tang that would be happy in my tank? Or any other types of fish that would do well? Nothing that will nip or pick on the others or eat crustaceans