hi this i have copied from skiflech
Wanna keep a Powder Blue Tang? My personal reccomendations are the following:
200+ gallon tank AT LEAST 8 feet long, prefferably 10
A true wavemaking device like a tunze wavemaker
An auto feeder providing the Tang's favorite food 4 times a day
A well designed auto topoff system to keep salinity stable
Use of a reef controller to maintain stable temp +/-2 degrees C
Twice daily feedings of nori algae
A MASSIVE skimmer and refugium to deal with all the excess nutrients from the required overfeeding
PBT's have VORACIOUS appetites on the natural reef and have MASSIVE territories. If you see one in the wild, I guarantee you'll understand as they swim CONSTANTLY over the reef, picking bits of algae wherever they can and moving along. In the wild their territories likely span for acres at a time.
So if you try and just plunk that thing down in a small glass box full of other fish and little food, they're going to do very poorly. As ben mentioned, they're Ich magnets because of their dietary requirements and space requirements. IMO VM, they're not suited for a smaller tank like yours.
Other fish I may suggest which are hardier and might tolerate your tank size would be Anthias/Psuedoanthias, Scribbled Rabbitfish, or a Naso tang if you really want larger colorful fish. Emperor Angels are another type that are possible, although not ALWAYS reef safe