i would quarantine the star fish. Dont kill it just yet, but you dont want it to polute the tank, just get a cheep pump and a fish bowl place it buy ur tank for light and place him in there maybe, idk it might make it worst, id call a really smart fish store i have one here in SC, that i ask a lot of stuff, but make shure they know what they are talking about

__________________
Glad to be of any help-Austin.