Potassium Iodide is an iodine "salt". It is just another way of getting iodine into the water. Elemental iodine is fairly chemically reactive and you would not find it in a pure state naturally. Because of it reactivity, it would be most likely found as a "salt." In sea water, iodine is bound up as a salt, not in pure form. Pure iodine in pretty rugged stuff, chemically speaking.
You know you are a true fish-o-holic if you can field strip any powerhead on the market.