The problem is that your tank is infected. So unless you remove all fish for 6 to 8 weeks, you have no cure. Hippo tangs are so easily stressed; they seem to be ich magnets.
I had such a problem with ich and I didn’t have a QT big enough to house all my fish. I was going to give up and just let them die...my last ditch effort was to give them garlic to up the immune system and warm the tank to 82, the tang is less stressed in the warm water.
It worked; the fish were able to fight off the ich. I did not add any new fish for over a year for fear of it being stressed and allowing the ich to regroup, and by sheer numbers kill everything.. As time passed I had to move, my 90g and all had to come with me. Very stressful for my fish. To my amazement nothing came down with ich..it was gone.
I attribute that to the fact that the ich parasite needs a host to survive. With the fish fighting off the parasite they eventually died off. Now this is all assumption, nothing from books. It’s just the way it worked for me. I have not had an ich outbreak in ...2 years now. Nor have I added but one fish in all that time.
To duplicate what I did..up the temp to 82, feed fresh garlic juice on the food (makes the tank stink) do not add any more fish for a year. If you only have the one fish...move it to a hospital tank and do hypo and leave the tank empty for 8 weeks.
The truth is I could have avoided all that trouble, if I had quarantined my fish like I should. An ounce of prevention is worth a pound of cure. Oh how true that is in this hobby.
