I have also found them to be Ich-sensitive fish, although a great joy to most larger aquaria. As with all tangs, they need a good vegetarian diet to be kept healthy. As tangs go, they are among the least contentious, and can usually be safely kept with their own kind or other types of tangs.
I agree with the above comments regarding Regal Blues: What a great reef fish! I recently bought one ("Blueboy"), and his outgoing, curious character provides endless entertainment. He is a chum to the Percula Clownfish ("Bozo"), and the two can be seen swimming side-by-side in the tank. Also, I haven't noticed any aggression between Blueboy and the Yellow Tang, who was introduced into the 340 liter tank at the same time.
I have had my regal tang for about a year and he has grown faster then all the other fish. He gets along very well with my yellow tang and I have not had a whitespot problem with him. I would say the powder blue is more suseptable to white spot, so if kept with the correct filteration and a good UV I think the regal tang is the best addition to any aquaria.
It's a beautiful fish, especially with those 2 different colors. It is very susceptible to ich like everybody has stated. The fish is not really aggressive and the most crucial period is at the beginning when, if you don't take care of it, it can die very easy. It's a beautiful fish if you are responsible with it.
My wife and I recently purchased a regal tang. We love the look of this fish. There is a major problem though. We have two cleaner shrimp that have done a good job of willfully cleaning all of our fish. The very same day we put the regal tang in the tank, he started eating the antennae off the shrimp. Ate them down to the nub. My wife just called me here at work and informed me that he has just eaten the legs off one of the shrimp so she is getting the shrimp out of the tank (we have a separate place in case there are problems between species) and we will be getting rid of the tang ASAP. We have read things saying to be careful with these tangs, but we haven't heard from any of the dealers in town (Wichita, Kansas) about tangs eating shrimp. The weird thing on top of this is we had a yellow tang about 4 weeks ago begin to do the same thing but only after he had been in the tank for over 2 months.
I haven't had much luck with this fish. I have had 3 of them (all at different times) in my tank. My first one was a big guy, he never adapted to my tank, never ate, got Hole in Head and died. My next one survived with me but I had to get rid of him because he was really aggressive and would never stop picking on my Yellow Tang. My last one was a little guy that died of Ich like 2 weeks after I got him. So from what I can tell, most of them are peaceful except for that one that I had, it's a challenging fish to keep, gets sick easily and could be difficult to feed.