Congrats! I'm doing a Rock Beauty too. (
thread). Exactly 3 1/2 months today....
IMO, there are two hurdles to Rock Beauties. The first is the one month'ish period. This hurdle is the 'I got a healthy specimen' period. Many RB's fail to adapt to captivity, and do not tolerate the collection process. The second hurdle is the 3 month to 9 month period. This period is where you know you've got their diet some what correct.
Yea, as Crimzy stated, for Rock Beauties, sponge is a integral part. Well, for any large angel, sponge is crucial, but it's thought Rock Beauty feed almost exclusively on sponges. I use sponge cubes from Ocean Nutrition, then with a food grater, shave off tiny slivers, since mine is so small. It took a good bit of time, and perhaps some guideness from my Blueface, but the Rock Beauty is now picking at the sponge pieces. I'm a bit lucky too, in that small juvi large angels typically don't start to eat sponge until they grow, in the meantime, they have a mostly algae based diet.