I will just throw in so it is not confused - they won't eat "algae" like nuissance algaes. They are "grazers" on various stuff on LR such as bacterial/algal films, bryozoans, encrusting sponges and similar. But I don't want people to think they can get buy with one if they just have algae or stuff to scavenge...if so, we could all keep these stars. I would still consider this to be a "bigger tank" star, at least 75g...until I hear from people with them in smaller tanks. Lots and lots of LR...mature tank...and a reef. I would also get one in all but the largest tanks....or keep one a year and then maybe try another later. One year is the critical point after the first month. We look for signs of starvation at 8-12 months.
Have you ever tried to see if it is interested in and spot or target feeding? That would be interesting to know. Nothing to go out of the way for, just as you regularly feed.