Trace Iodine question

[Wendy]

I am new to corals and still trying to figure everything out, i was reading on some of the corals ive been thinking about getting and it mentions that some of them need trace amounts of Iodine.How do you give them the iodine? will the iodine affect any of my fish/shrimp? is it weekly or bi-weekly they'll need it? and lastley is there a preffered kind of Iodine to use?
Sorry for so many questions,i just want to be sure that if i do get corals that i can care for them properly