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aterina stars, they aren't a problem. if you ever see them on your coral, then its time for them to go. they can overpopulate your tank, if you are over feeding or there is lots of algae/coraline algae for them to feed on.
I'm having a break out of them too. Only about 5% of them are coral eating varieties. A black banded harlequin shrimp will eat them and unlike the regular harlequin, it won't starve once they are gone. But they are easy to scrape off the glass and net.