This was posted on a local board by a guy that I know well and whose opinion I value. Carolina Aquarium Community Forum :: View topic - Flatworms that eat Ricordea, Caulastrea, leathers, xenia,etc (http://www.carolinafishtalk.com/forum/viewtopic.php?t=2655&highlight=)

They are tough little boogers to get rid of!!! I treated with Flatworm Exit twice in 3 days, the first treatment killed my Purple Tang....they are STILL hanging on! I got a Six Line Wrasse and he's keeping them in check!