Had mine like 3 weeks, now. Was in perfect shape from the start which I think is key. No sunken stomach....it wouldn't eat anything that I fed it, only graze on algae on glass, floor, and rocks. I then had to try soaking nori in a cup of tank water, then when soggy, grind it up with my fingers into bits, tiny bits. It would eat that, then I used bigger pieces like the size of half of a pinky nail, again a bunch of them (20 pieces like this) in a little cup of tank water and then would pour it in a bit at a time and now it will go for these larger pieces, but only after 3 weeks. Won't touch anything else. It is about 2.5" long, got a touch of ick the 3rd day introduced, but went away in another 2 days. It did try to punk my new 4.5-5" emp angel, but now is chill again grazing all day.
Got to get a healthy, non-shrunken one from the start to be able to ride through the new adjustment period of being newly introduced, then it comes around.