If its a regular blue tang it requires a 180g tank, six foot long. A caribbean blue can go into a 125g 6 footer.
All the fish I buy come from one store, except for some ORA clowns I had. Is it possible to isolate the tang in another tank just in case?
I'm sure the seller didnt' purposely sell you a bad fish, but even the nicest shops can have issues. Like I said, almost every fish I;ve bought came from the same place and the caribbean blue tang that caused all my fish to die came from a reputable store. Identifying if anything is wrong is the first step. isolation would be a good idea as I said.
You don't wanna treat your display tank with anything by the way, it could affect inverts forever in your tank as the live rock absorbs those chemicals.
if it were me and I couldnt isolate it I would keep the lights off and let it try to settle in to it's new home. Tangs are really tough in certain ways.
How long did you acclimate for btw? A quick one might have stressed it out a bit.