i never meant to start an arguement serpentman... im sorry you felt that way...
i used to do tank maintenance for a lfs near me... when i started, i saw all kinds of unadvised stocking... i know one guy who still has a yellow tang in a 24g bio cube... but to them, i knew nothing and they knew everything... or jus didnt care enough to comprimise their own eye candy...
again, my point here is particularly blues, but since the 20gl statement came up, i would add... i know 3 people from taht job who have yellow in something less than a 24" tank or a tank of 30 gallons.... none of which had any good filtration... im sure the fish wont lat unfortunatly... and soooo many people had blues... but thankfully they were all in nothing less than 100s of at least 4' or bigger... alot of foolish people with big angels in small tanks though...