I have the Seachem Iodine test -- it's a bit complicated and I have trouble registering anything.
Best thing is water changes of course. But sometimes if need be, I may supplement but at just half of the recommended dose, using Julian Sprung's Sea (trace) Elements. Between wet skimming I do sometimes based on needing to export and the crustaceans that need to molt, I feel comfortable supplementing this way -- if I haven't done a water change say in at least two weeks time. Then when I do a water change, I use more aged seawater than normal. YMMV