It's difficult to find, but talk to any invertebrate zoologists. You can try a search on crustacean molting and iodine, but there's nothing there, because there is no correlation. The only thing you'll find googling it is from hobbyist websites, not peer review texts and journals. It is an creation of the hobby. It was never something that was proven to begin with. There is one study that proves that dietary iodine is important, but it is for many things. Plus, most foods have plenty of that--freshwater and marine.