I have them now and I have found that regular siphoning is about the best mitigation there is. I did add a spotted mandarin and was planning to add a 6 line, but between the mandarin and siphoning, I can deal with them. There is a flavor of flat worm that will eat SPS
but luckily not what I have. Though, they can quickly cover zoos and other softies which typically cause them to close and, in extreme cases, starve due to lack of light. Again, I find if I just siphon them off the coral, the coral recovers just fine. I have read alot about the Flat Worm Exit, the common complaint being that people use it and they lose a bunch of other stuff in the tank. The reason, I have gathered, is that when you have a true infestation of FW
's the sheer number that die and release toxins into the tank while treating cause death. So, if you really want to eliminate them, I would consider siphoning as best you can then treating, being prepared to do a large water change and using some carbon for the following week. As for me, given that the new mandarin seems content with picking at them, I will keep them around and just siphon. It encourages other, generally good husbandry anyway. GL!