Quoted from CR Brightwell's "Marine Chemistry":
"Iodine may very well be one of the most important elements present in a reef aquarium; it's concentration is usually a limiting factor in the rate of metabolism and growth of fishes and invertebrates. Without a sufficient concentration of iodine in the water, fishes will often develop goiter, crustaceans will not molt, certain types of macroalgae will not survive, soft corals will gradually die, corals in general will show poorly (iodide affects pigmentation) Xenia and Anthelia won't thrive and may die back, and the list continues. Iodide may be very important to hermatypic invertebrates as a means to help detoxify excess oxygen produced by their symbiotic zooxanthellae under supraoptimal light.... It's important to note that overdosing (iodine) can have disastrous effects on an aquarium system; an overdose of iodine can kill beneficial bacteria and destroy sensitive tissue, leading to the rapid demise of the system's inhabitants...elevated iodine concentration in the presence of other required nutrients can encourage the rapid growth of cyanobacterial sheets...A range of 0.05 to 0.08 mg/L of ionic iodine is acceptable for both fish-only and reef systems...Should there be a need to rapidly decrease the concentration of iodine in a marine aquarium, there is no faster way that with one of the aquarium supplements formulated to detoxify chlorine, chloramines, and ammonia..."