Flatworm exit scares the hell out of me. Those puppies are toxic as hell, especially when they all die all at once! I had a flatworm problem 7 or so years ago and used it. I was well prepared, siphoned as many dead ones as possible, and did water changes at appropriate intervals afterwards. I immediately had about every problem known to man in an SPS tank including the death of a couple of my favorite colonies. So, if I were u, I would exhaust every possible natural solution before using that stuff....but trust me, it works!