Kill em off with Salifert Flatworm Exit ... Follow box directions to the letter, scoop out what you can with a brine shrimp net, put a extra heavy load of carbon in your water column, and do a 50% water change. I had to do this 3 times over the course of 6 months to finally be done with them. Get a Six Line Wrasse too ... They eat them ... Mine did. Good luck !