I have a cowfish, it has a puffy cottonballs growing on it , at the store they told me it is a virus I was suppouse to change a water which i did 2 days ago. It is like that for 3 weeks now,lately my tang gat same way it lost a color and today it was not eating.
IMO -Sounds like ich. Several ways to treat all depending on what else is in your tank. Ich is primarily a stress related disease. If ich not sure what a water change will do, except for routine chnges, it maybe only stress out more.
Sounds like a Fungus to me. we had a leatherjacket in the aquarium with a fungal infection. Water baths won't work if it's developed hyphae (the reproductive/spreading structures) which yours probably have if it's spread to the tang. You need to treat with a good antifungal (check for copper if you're planning to put an octi in the tank at any stage!).
Lymphocystis? correct answer. Saltwater Ich or Velvet (Oodinium) ? wrong answer!
If the description as cotton-ball like stuff was accutate, it is most unlikely to be ectoparasites such as Oodinium or Whitespot (Ich). Lymphocystisis was described as a viral disease. Apparently, it is not leathal but was nonetheless unsightly. Some claim that it was related to the chemical composition of the seawater in the tank (depends on which brand of seasalt (if artificial seawater was used). I have success by manually scraping it off followed by a touch of antibiotic solution. Such handling 0f the fish (out of water) was extremely stressful to fish and had to be done quickly and skillfully though.