An example of Ophiura's advice about starfish
Originally posted by ophiura
BigMac is right, there is no food that you can buy for them. You must have a large, mature system with a lot of live rock (eg at least 55 lbs in a 55g, and that is minimum, IMO). You also can not have any similar starfish in the tank (eg no Fromia stars...or generally any of the 'reef safe' seastars), unless you have tanks in the 125g and above with 125+lbs of LR! Best success would be with one, keeping in mind that healthy happy Linckia will readily reproduce in large systems by dropping arms.
These guys feed on algal and bacterial films, sponges, etc encrusting the LR. While it seems there would be an unlimited supply, imagine how much bacteria and microscopic algae you would have to eat each day to meet your nutritional requirements. LOTS. The same is true for these starfish. So, if you do not have a lot of LR, it probably will not survive. They typically starve to death in a few months to a year.