Check my journal on Potassium
I would also advise caution with potassium -- unlike magnesium, it's quite prevalent in the horrible average American diet, even to excess. I know it's expensive and hard to find someone to do it, but it's good to get potassium levels before supplementing with it, again unlike magnesium, which unless you eat a ton of fresh green leafy vegetables most of us just don't get enough of anymore. It can help many people, but just sayin'. As to the form, that really depends on the person. Any good health food store will have potassium in absorbable form. Potassium iodide is an iodine supplement, not a potassium supplement. Every mineral must be chelated with something to be absorbed properly, but the chelation agent will be broken off more or less efficiently in different people.
I have since learned of the possible danger with excessive potassium.