A powder blue tang will not fit in a 4ft tank. They need larger aquariums that are at least 6ft long. For a 4ft aquarium look into kole tangs, tomini tangs, and mimic tangs.
I have a powder blue and mine is 4x2x2ft
Yellow tangs are the easiest to keep in a smaller tank from what I have read. Mine seems to be quite happy in my 90g. http://saltaquarium.about.com/od/tangsurgeonfishprofiles/p/pryellowtang.htm
Im sure that site can give you the info your looking for on other tangs as well.
Found a link with many tangs: http://saltaquarium.about.com/od/tangsurgeonfishprofiles/tp/tangprofilehub.htm
Kole is also a very popular tang from what i read.
My 5" powder blue has been in a 4' tank since I got him. He hasn't grown at all over 5+ years. Threads on the topic show lack of growth regardless of tank size, so I'm not sure what to think. From my personal experience, I cannot say that PBT need larger than a 4" tank.
I'm not quite sure what "easiest to keep in a smaller tank" means. Maybe the context of the sentence is being lost the way I'm reading it aloud to myself. This is definately NOT the case. I would also avoid About.com, though it provides some basic information, I would do most all of your research here and at your LFS and through literature.
My 5" powder blue has been in a 4' tank since I got him. He hasn't grown at all over 5+ years. Threads on the topic show lack of growth regardless of tank size, so I'm not sure what to think. From my personal experience, I cannot say that PBT need larger than a 4" tank.
I highly value your opinions, but his growth may be stunted.
x2..had mine for over ten years in my 90(4ft) before I upgraded...it only got ich once in all that time...water quality and diet go a long way in fish health.My 5" powder blue has been in a 4' tank since I got him. He hasn't grown at all over 5+ years. Threads on the topic show lack of growth regardless of tank size, so I'm not sure what to think. From my personal experience, I cannot say that PBT need larger than a 4" tank.