I'm not so liberal on tank sizes; IME the activity level of this fish deserves a 4x2x2-120GL or a 6x1.5x2-135. They can obtain a foot in length, and for anyone who's seen a foot long fish in a 90GL tank would probably agree. My LFS has a 12" Desjardini Tang in a 90, and it looks sooooo tight it's sad. I've got a 54"x18"24"-100GL Undy tank, and I'm hopeing to swap it out for a 120 or 135 sooner than later. People fixate so much on the length of a tank, but IMO haveing the width is equally as important.