We finally got our UV up and running so thought we would try to start tangs. Introduced 3 to our 180 gallon. One of them was a very skinny mimic tang. After 3 weeks, we never saw him again so assumed he had passed. LFS said we had a huge cleanup crew so monitor levels but do not tear apart tank to search for him. A week later we noticed some spots on the bristletooth. He died 2 days later. That same day our Blue spot anthias died and our clown fish was hiding under our huge devil hand so I could not get a good look at her. She died a couple days later. That day our engineer goby came out and looked like it was struggling and looked like it was shedding. Gathered him up and took to LFS along with water sample. They said if they had to guess it was Brook and water was perfect. Told us to pull remaining fish (5 chromis, 1 clown, sailfin, orange back fairy wrasse, fire fish, mandarin dragonet, pink spot goby, coral beauty, filefish) and treat with formalin but the treatment would probably kill them all, and to go fallow for 4 weeks. While trying to set up a large enough tank to put them all for treatment it has now been a week. No fish are showing any signs of disease so my questions are: was it brook? Is there anyway to treat without more than likely killing them since they do not appear ill? Sailfin might have a couple little speckles in him.