I agree, he might not feel safe without the safety of numbers. How long has the tang and damsels been in the tank? Those guys can be on the mean side, specially the damsels. I know my yellow tang harasses most fish i add for a while so he could be making the anthias uncomfortable as well.
Maybe changing some liverock around would help? And keeping the whites off for a bit maybe? thats what i did with my squareback anthias, he was super scared and all he did was hide behind the rocks. I kept the lights on blues for a longer period of time each day and after a week or so he started coming out more.
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.