I never owned Any tangs but what I see from other threads and guides on fish sizes Is like a scopas tang most agree could go in a 90 gallon.
Some say some other tangs at a push like yellow tang could go in a 90 gallon but if see signs of stress then give away to lfs/ another reefer or get a bigger system.
Short term as tangs are juvenile and like 1- 3 Inch big,some say can temporary keep in a 90 gallon system but then upgrade as they gain more size .
But end if day its your tank and hopefully you done research on how to set up your tank and make less stressful for all your livestock like your aquascape got caves for fishes to retreat to if needed or sleeping quarters, under hangs and over hangs and fish can lose sight of each other as swimming around tank ,depth of sandbed if got wrasses that go under the sand and the basics like this and compatability of your livestock so aggression is a minimised and use if acclimination boxes if introducing fish that may not like new additions and the like.
My personal view is if done your research and you put a fish in tank and have a back up plan if initial idea doesn't work and new fish isn't stressed and got ample rockwork to graze and fish comfortable and no stress signs then just see how it goes but if I wanted say a blue tang ( dory fish ) and had say a 50 gallon tank and a few people said kept it in a 50 gallon for its life time and seemed to be not stressed but then read 100's of people saying its way to small a tank unless keeping it in for few months then upgrade I would trust that many people have tried before me and fish was severely stressed in that size tank so I wouldn't even try.
But for others to help you.maybe say which tang you wanting to add to your tank and say age of tank and possibly a full tank shot picture would aid people .
Also length of your tank plays a good part in your decision as longer the better
Good luck ^_^