It seems through my research, that if anywhere down the supply or shipping chain the star is not properly acclimated, they can, and most likely will, go into osmotic shock.
It seems that they dont eat much, mostly detritus, but other sources indicate bio-film and sponges.
Any chance you could return it to its source ? Maybe in a good aquaculture facility such as Inland Aquatics, they could get it back to health, and you wouldnt be facing an untimely loss. Give Morgan a call at 1-888-368-9114, and ask him. He is a great guy, and an absolute expert on such things. Good Luck.