How did you acclimate it? These are the most delicate of the reef safe stars, and require 4+ hours of acclimation in order to have the best chance of survival. They are extremely prone to dying from acclimation shock. Tank parameters must be pristine, with specific gravity around 1.025; watch for fluctuation in pH and alk. If, in the next month, it starts to develop whitish patches on the arm, and basically looks like it is disintegrating, it is dying from salinity shock.
They do best in tanks 100g+ with at least that much LR and no other similar stars (basically do not get any other 'reef safe' stars except brittle/serpentstars). They feed on algal and bacterial films, sponges and other encrusting animals on LR and cannot be spot fed anything else in most cases, though they may be attracted to a dead fish in the tank. It is very important that the tank be large and mature, because these guys need to eat ALOT of bacterial and algal films (meaning they will not eat macro algae) in order to survive and it requires a good amount of time to regrow in areas they have covered.
They can often die at around the one year mark; success with these stars for a few months or a year is not a success. A majority of those collected for the trade die within a month of capture, if not sooner.
It is safe, but for more delicate than your other star. Keeping it alive is indeed the trick now. IMO, a 29 is way too small for this animal. Do a search for Linckia also spelled Linkia, and you should find a lot of info.