We will need more information to help you. How big is your tank? What is your current stock list? It's true that Tangs are more prone to Ich than many other species. Before you buy a Tang, it's a good idea to set up a quarantine tank. There are many threads on Reef Central regarding quarantine procedures. It's the only way to prevent new fish from infecting existing ones.
Your tang should be pretty much the last fish in the tank (other than triggers, etc.) as they can be very aggressive to subsequently-introduced fish.
Make sure to quarantine all fish that you put in the tank, and then get your tang, quarantine it and put it in the tank. You want to ensure that there is no ich in the tank when the tang gets there.
I'm going to let the tank sit for a few months before anything goes into it, All I put in there is just a mushroom from my smaller tank.
I have some liverock from my other tank, I want to transfer into the new tank. the rock has been in there for 2 years so I dont have to worry about it being cured. thats a plus.
does anyone know why tangs are prone to ich compared to other fish ?
thanks for all the help so far.