Zoanthid-eating Nudibranchs are difficult to see. As they eat the zoas, the color they injest will enter their bodies, so they blend in perfectly. Your best bet is to look at the zoanthid colonies at night when they are closed up, as the nudibranchs can't hide then. If you choose to dip zoanthids in a solution of saltwater and iodine, you may spot these litle guys hiding within the polyps. They are predators, and should not be introduced into your tank. NOT Reef-safe