i've been using melafix marine as a aefw dip. It seems to have that critical balance of not too harsh on corals while definitely bad for pests. My usual procedure is to dip the frag in a bucket in a melafix solution, then to soak / rinse it after that in another bucket of tank water before finally returning to the tank. With melafix, i see flatworms in the dip bucket but not in the rinse bucket (they've already all let go and been dislodged). With coral rx, while there are flatworms in the dip bucket, sometimes there is a flatworm or two in the rinse bucket, which makes me wonder if they were all dislodged / removed during the treatment.
You could also use iodine preparations, such as drugstore povidone or tropic marin pro coral cure. I find them effective though a bit harsher on the coral, depending on the concentration.