Most people will say no. A juvenile (perhaps starting roughly the size of a quarter) would be ok in a 55 gallon for a year or two but a medium sized tang of any variety will need more space to continue to grow. Again, most people will tell you that a Regal Tang (aka. blue hippo) will need at least a 6' tank. I think the starting size for that length is 125 gallon, though I could be wrong.