The first one I had lasted about 2 months, was eating the whole time. Woke up one morning and it was dead.
My current one has been with me for 7 months, and eats like a big. IMO, it is important to have an established tank with aged live rock for them to pick at. Mine is grazing on the rocks and back glass all day long. Mine has a fondness for Spectrum pellets, LifeLine's herbivore mix, Rod's food, and mysis.
Also, I wouldn't QT this fish, feed that a QT would be too sterile for them.
Here is a recent picture of mine.