Some information from Bob Fenner on Chocolate Chip Starfish.
"These are actually voracious eaters. More than one will be quite the bioload. They easily grow to 6 inches in diameter. They can be difficult to keep alive due to nutritional issues feed a variety of chunks of marine fish, shellfish, and crustaceans fortified with Selcon and vitamins. They are not reef safe--they will eat all sessile invertebrates and any mobile ones they can sneak up on and capture. Remember to acclimate over several hours. (Some starfish species, such as Linckia laevigata, need to be drip acclimated over 6-8 hours. All starfish require excellent and stable water conditions. All are very sensitive to fluctuations in pH, oxygen or salinity for example. They will also be harmed by excessive nitrate. Read as much as you can about them before buying. I've tried a lot of starfish over the past few years, and I've decided that most of them are best left in the sea. I would not recommend other species that you may come across in your research and shopping. Truth be told, the Chocolate Chips don't have such a great survival record themselves."