I currently have a 3.5 inch regal blue (aka hippo tang) in my 46 gallon. I got him when he was about 2 inches just over 6 months ago.
The tank's OK for him now, but I suspect he'll be much happier in the 135 I'm planning out right now.
Regals are ich magnets. You MUST MUST MUST have a Q-tank if you purchase one because it'll almost be guaranteed to have ich.
I think the whole HLLE thing is mainly as a result poor diet. You must feed them a mainly vegetarian diet. This means LOTS of nori (dried seaweed), but NO lettuce (iceberg, romaine or otherwise) as it has no nutritional value. I also feed Formula 2, mysis shrimp, daphnia, spirulina enriched brine shrimp, cyclopeeze, chopped clams/scallops and supplement with Selcon and a drop of garlic juice as an attractant.