I agree with Carey, but I think you were asking about supplements, not feeding. If you are not an expert, you will, most likely, kill any coral that isn't mostly fed from symbiotic algae...period.
As to iodine, she is right, don't add what you can't test for, but it is almost impossible to overdose iodine or many of the other supplements. It is also not necessary usually. If your tank is packed with corals, then yes you might need some specific supplements, but in almost all cases, weekly water changes will be all you need.
I do, however, soak my food in Reef Complete to try and fortify what I feed.