Purples tend to be on the aggressive side and IMHO definitely need a 6 foot long tank, I agree with the recommendation of a One Spot Foxface. I would get the Kole and a One Spot Foxface as a compromise to the Yellow Tang. It will perform a similar function, give you a yellow fish, but it will be significantly more likely to be well behaved. That and they go night camo at night and can alter color based on mood. I replaced my jerk of a Yellow Tang with a One Spot Foxface and have been much happier with it.