45's are often a tall 30 long, so a 3 foot tank. Not always, but that is what mine is. While it might work for awhile, it won't work for years, IMO. They are a very, very active fish.
FWIW, I would be wary of an LFS that pushed brine as a primary diet. AND certianly one that couldn't answer basic questions about the fish. I wouldn't trust their quality, I would trust their advice, I wouldn't buy the livestock, I wouldn't give them a dime. JMO. If you are in the fish selling business, you better be able to answer questions about the fish you sell. Still, JMO
. No back to brine - though quite delectable to many fish and a good way to get them to eat, is basically nutritionally devoid. It really should be soaked in Zoe, Selcon or similar at the very least. But as mentioned, tangs need greens.
I must give one slap on the wrist
But I promise a gentle one
...a good price is not the best way to choose a fish. You may definitely get more than you bargained for...especially because so many fish are very pretty and tempting but a waste of your money - regardless of how inexpensive it was.