Star Fish

Going to guess theyre Asterina stars. You could pick them out and hope you get most of them, or a harlequin shrimp would do a good job.

Are they hurting anything? If not, why be so fast to get rid of them?
 
What kind of starfish are they, small brittle starfish or asterina stars? The brittle starfish are a great part of your clean up crew, you'll want to leave those alone. As far as the asterina stars go, I think the jury is still out on whether or not there good or bad for a reef tank. Either way though, if you want to lower the population your going to have to manually remove as many as you can.

http://reefkeeping.com/issues/2004-06/ac/feature/index.php

http://reefkeeping.com/issues/2004-12/rs/index.php
 
+1 to cloak. Anecdotally, only about 10% of asterinas are truly harmful (typically zoa eaters), so most folks just keep an eye on them to see if they're hurting anything. If not, they're kinda cool looking. I just bought a harlequin b/c I've now got too many of the little buggers in my tank at the moment. If you do get a harlequin, keep in mind that you'll need to find it a new home once the asterinas are gone unless you have a fairly large tank that can replace asterinas as fast as the harlequin is eating them.
 
Truthfully I think the idea that Asterina sp. eat coral is over exaggerated. I'll concede that some may nibble some coral, but I've never seen any good evidence in person or read any accounts on here that really made me beleilve they're a problem. No need to jump to conclusions on a simple possibility. They're easy enough to catch and remove if they ever do truly become a problem.
 
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