They'll all outgrow that. I hear a Kole tang is a tang you can keep in a smaller tank, but not that small. You can get some very young tangs and keep them for awhile until they outgrow it, if you're so inclined. I see 2-3 inch sailfins at my LFS all the time that I think would be fine in a smaller tank for a reasonable amount of time, but I'm sure more tang-knowledgeable folks will disagree. People on these forums are very big on lots of space for tangs (as i take it they should be).