First, there are no reef safe treatments. Second, if one fish has it, all potentially have or will have it. Many tanks can do fine with ich in the system, never seeing an outbreak, but it's still there waiting.
The only real way is above, removing all fish for treatment, and leaving the tank empty for 3 months. Otherwise, it's a gamble.
I once had an ich outbreak, fed heavily with garlic, and it went away for years. Another time I had an outbreak (recently) and lost most of my fish. So, you just have to decide which way you want to go
