Salifert Flatworm eXit Test Kit (Reef)Flatworm eXit itself is quite safe to fish and invertebrates. However, the body fluids of flatworms can be toxic to some reef inhabitants when present in a too high concentration. This body fluid is sometimes excreted when flatworms die. So when you use this product it is important to do the following first 1] Siphon out as many flatworms as possible. 2] Keep sufficient fresh activated carbon in a canister ready. 3] Turn off UV, ozone and remove