To be honest stars are still fairly un-known. Except for the ones that are dedicated scavengers we still don't know 100% what they eat or how much. One draw back to stars is that they require exquisite water quality. There entire body is hydro-vascular (or something like that) so the water isn't just around them it also supports their bodies and systems. Some stars can be exposed to water but many can NOT! Those that can't will literally melt over a few hours after being exposed and dissolve into mush. They also require and delicate and extended acclimation when you get them. I use Drip Acclimation for everything now but they really do need this always.
Another thing about stars is most have a relatively slow metabolism so if they are starving they will do it over a long period of time. Usually if something is off you'll notice small abrasions like they got cut or something and then they'll drop a leg here and there and just vanish.
They are really cool creatures which I love to see but know they are still some-what unknown in our industry.
Good luck and happy reefing.
Allen
