I'd like to mention too that not all flatworms are equal, and most don't need to be nuked. As far as I can tell, it is mostly the larger acoel variety as pictured above that are the main issue (and acro eating FW's).

I had some smaller tan FW's and got all excited and FWE'd my tank, it killed a lot but didn't knock them out. They rebounded a bit, but now I don't see any anymore. Wasn't worth the money or the effort.

I've also seen 2 other types in there (the ghosties at night and one other type).