The information in this article is by large the result of my 22+ years of experience observing these animals in my own tanks, as well as tracking the results obtained by other hobbyists during that time.

More... (http://www.advancedaquarist.com/2008/1/fish)

Although this article is about angels I believe that much of the discussion about the psychological stress a too small tank imposes on these beautiful fish is applicable to tangs as well.