Tank size requirements for PBT herd

[christyf5]

Ok I thought I'd just throw this out there for fun. OA has 3 good sized powder blue tangs in right now in one of their coral tanks. They're such gorgeous fish and seeing the three of them is giving me ideas. I've always loved these fish and added a smaller one to my tank a couple of months ago and after a bit of reorganizing of the hierarchy he's fit right in.

Anyway, my question is, what kind of tank size would be suitable for these fish? I know they get large, need their swimming room etc. They seem to be treated "differently" than most other tangs because they are deemed harder to keep. Are they really that special or just like other surgeonfish/tangs in terms of environmental requirements?