At the risk of angering the tang police, who will say no...
...it can be done as I'm currently doing it. I have a pretty one (she's about 3 1/2" now) in a 55g. Not ideal, probably, but she's happy. Just make sure you don't have a super tight rock work. They like to swim about constantly and graze off the rocks. Mine is always scurrying around munching on the rock work, swimming in and out of the various caves and arches I have. Pretty much doesn't stop buzzing around till the lights go out. I definitely don't have the whole 1.5 lbs of rock per gallon thing going on...there's lots of open space for swimming in my "small" tank. She can circle my entire rock structure on several levels and has dug herself a little cave to sleep in at night that she shares with my firefish. It's an odd but cute pairing as she outweighs the firefish 5 to 1 and could probably swallow him in 2 gulps.
As Albano said... eventually you might have to give it up (as I may too) or upgrade to a bigger tank (as I'm already planning...185g next year, I hope...someone give me some $), so keep that in mind. You'll know if you see her behavior change to laying about a lot or combat.
Got mine from Live Aquaria Diver's Den. Arrived happy, healthy, and hungry. Eats everything I put in the tank, though at first didn't take to seaweed sheets and seemed to subsist on grazing for a few weeks. Gets along well with the clownfish, chromis and firefish, except for the one chromis who thinks he's a tough guy.
Diver's Den had a juvenile last week....I think she was like 1 1/2".
Honestly if I were you I'd skip the chromis just get the Kole. Or get the Chromis and not the tang if you are worried about the future. The more room, the better.
