I add a bit of Seachem's reef iodide - not iodine (used for treating wounds) - after water changes, less than or no more than single-dose levels.
I have no justification for doing so other than anecdotal evidence. Quite some time back I was keeping several Macrobrachium densonii (sp?), and was losing them one by one, always in molt. It was suggested to try the iodide, and the single survivor continued for normal life span. So I accepted that some shrimp at least have molt problems that may be helped by iodide. Frank Greco of the shrimp mailing list (and a great source for oddball shrimp) suggests using it as well. It may be myth, but I have bought into this one.
FWIW, YMMV.