I never had much luck with a six-line wrasse. I tried several different wrasses that were "flatworm eaters" and the only one that I have had any significant success with was a green tail spot wrasse (Halichoeres melanurus). After fighting them for years, including several treatments with Flatworm Exit, the tail spots have both of my tanks flatworm free. One of them came from another MAASTard after he had cleaned his tank, and the other cleaned out a tank at an LFS. I'm a believer.

I think a lot of the wrasses in this family (Coris wrasses) will eat some flatworms but few will make a steady diet of them to the point that they are eliminated, or nearly so. I've tried six-line, yellow coris, leopard and tail spot. All were reported to be good flatworm eaters. I also tried both species of mandarins. I can't say they are 100% eliminated, but I can't see any in my tanks. If you look at some of the old pics of my tanks you can see plenty of evidence of flatworms.

http://www.fishbase.org/Summary/spec...name=Melanurus