No, because copepods, amphipods, etc. are in an entirely different phylum than flatworms. IME, and I've used it a lot on a large scale, it will only harm flatworms or their cousins; however, it does not even kill all flatworms. It does a great job of killing the ones you seem to have a problem with. IME it did not harm micro brittle stars, copepods, amphipods, fish, snails, or any other inverts. If it does it's most likely not the drug and more likely the flatworms disintegrating into your water. Make sure to follow the instructions carefully and ramp up the does slowly if needed. Definitely use carbon and have a water change ready to go (although I never found this necessary but is a good practice. If you use enough carbon you should have no problems).
