This looks like itch.tangs are prone to this.learned from my reef buddies can be from stress as well. Some advise to run uv.but when u run uv,it might also kill off ur good bacteria as well...thus unsure this will not create more issues..however the best is to ensure they eat as during this itch period they will might or might not eat well.there is also a write up on itch bro.u might wanna read them up... Sent from Singapore Reef Club mobile app