Flatworms can be detrimental to any reef tank. Flatworms can harm corals in several different ways. They can consume them and they can prevent light from reaching them. Don't take chances if you notice a flatworm infestation in your aquarium. Flatworm Exit by Salifert and Flatworm Stop by Korallen-Zucht have been use by hobbyists for years with great success. Be sure to follow the instructions on either product. As flatworms die they can potentially release a toxin into the tank that can have a negative impact. Should you have any further questions please contact us.