This is a good read, saving for future issues.to be more specific on the type of flatworm. You have Red Planaria Flatworms.
http://www.melevsreef.com/node/651 describes how to get rid of them.
What wrasse will take care of them? http://www.reefcentral.com/forums/showthread.php?t=1891040
Is everyone sure they aren't just being eaten by the fish when they make it to the display tank?