Reef•Basis Sustain Iodine is a unique, multicomponent iodine release system, designed to nourish organisms that require iodine. It is particularly useful for soft corals of all kinds, particularly xenia, as well as gorgonians, hard corals, tunicates, marine worms such as feather dusters, sponges, macroalgae, and crustaceans, particularly shrimp. Iodine, while present in better salt mixes, is rapidly removed through ozone, skimming, carbon and other filtration and used up by inhabitants. It is necessary, therefore, to supplement it for maximum invertebrate and algae health, particularly if you have strong lighting.