Larry,
I had flatworms in my tank by hundred and tryied many things,lowering the temp in the tank does help to stop or slow their spawning cicles /syphoning / and I have a six line and a lepard wrasse there are some products out there but personally I wouldnt put any quemical.
You do want to be on top of this before it get get out of control ???
I still have some few around but very few.
I would definatelly pay the money for the "Chelidonura Varians." but they are hard to get.
Iif TRT has them or can get them let me know. ::
~Rob