I have a sixline as well, and I never saw him eat any flatworms when I had a small problem with them. I agree with siphoning them out as a first attempt at getting rid of them. My guess is if you see ten there are a bunch more you aren't seeing. Flatworm exit fixed my problem and really wasn't a very difficult treatment. They were all gone in a matter of a half hour. You just have to make sure to siphon as many as possible, do a nice size water change, and run some carbon after the treatment.