Toxic Metal Sponge, 250 ml., Kent Marine. Toxic Metal Sponge is a regenerable, bead shaped resin which safely removes heavy metals. It is safe for use in all aquatic systems. Removes copper, lead, mercury and other heavy metals from marine and freshwater aquariums, and tap water. Toxic Metal Sponge contains special form macroporous cation exchange resins. Regenerable over and over again. Light beads turn a slight blue or gray, indicating exhaustion and need for regeneration. Resin life is about 2 years of service.