here is an option that worked for me, but I wouldn't recommend it because it goes against most trusted leaders in the reef field. I can say that It 100% definitely worked for me. At the time, I only had soft corals in my tank, and I did not have any STONY corals whatsoever! ALL fish recovered 100% due to this treatment. It was not from luck, immunity, or whatever. My tang is now 2 & a half years old, but was near death at the time Almost all of my fish had it at the time, and all recovered that were alive at the start of the treatment. I know there are solutions that work 100% of the time, unfortunately, this is not one of them.
1) I installed a UV light. (it has since been removed)
2) I used "Reef Safe" Kick-Ich. (quoting from marine depot's site) It is a water treatment for the control of ich (a.k.a. "whitespot disease") in marine and freshwater aquaria. It has been scientifically formulated to eliminate the free swimming, infectious stage of the ich life cycle while being safe for all freshwater and marine aquaria. Kick-Ich has a long shelf life at room temperature and is supplied in easy to use, self-dosing bottles. Safe for all fish, corals, invertebrates and macro algae, as well as the facultative anaerobes and nitrifying bacteria essential to biologic filtration.
3) I talked directly with the owner & used a higher dosage that compensated for me running a skimmer for 12 hours a day. i also DOSED TWICE after a 2 week break.