I use Icelandic kelp for my iodine intake - potassium iodide has a -lot- of iodine and should only be used if you are in a severe radiation zone. I have no thyroid issues, but there is a noticeable difference if you are iodine deficient. I would recommend taking 1 225 mcg (iodine)/ 41 mg (kelp) pill every other day to prevent yourself from overdosing.
Most adults can take up to 1000 mcg/day safely, and 900mcg for pregnant women. Overdosing on iodine can shut down your thyroid, so I just like to supplement on the lower side for safety.
Please forgive me for sounding rude here but I must call this out. Given that the body will excrete any excess iodine the limitation of 1000mcg isn't accurate. While the US RDA is in the order of 100-250 mcg (depending) that is the minimum required to prevent goiter. It doesn't help one achieve "optimum" health. Most iodine supplements vary in range from 12.5mg to over 100mg and are taken regularly as a supplement. The amount of iodine a person needs is determined not by a standard established over half a century ago but instead by your own body, health, stress, genetics, etc. In fact, people who eat a lot of sea vegetables will naturally consume over 12 mg of iodine a day. So, again recommending a limiting supplementation level for those who do not consume sea vegetables and loads of shellfish isn't practical. As for me, I take Potassium Iodide 50mg does the trick, but you may be different.. However, if the concern is a fully functioning thyroid and body overall you have got to consider selenium, zinc, tyrosine, magnesium, copper, etc. Iodine if found in greatest concentrations in the thyroid, breast tissue, ovaries and testicles (obviously depending on gender).. In fact for women who are very large breasted their concentration of iodine in the breast may exceed (likely) the 50mg of iodine stored in the thyroid. So again, how much is a question that would best be answered by your Dr. based upon the results of an iodine loading test. However, if you are supplementing I wouldn't be overly concerned (unless there are specifically concerning health factors of course), by limitations created by the USRDA or other governmental body. Most of their recommendations are either outdated, were completely inaccurate to begin with or were established to create a MINIMUM threshold. For example, the USRDA for vitamin D is 400iu. Which is enough to prevent rickets. However, your body will manufacturer tens of thousands of IU's a day if you are in the sun so which one's accurate? The gov't or your own body?
This guest post on the Perfect Health Diet site, suggests that kelp may be sub-optimal due to other things it contains: http://perfecthealthdiet.com/2011/05/iodine-and-hashimotos-thyroiditis-part-2/
In Paul's supplement recs page he recommends potassium iodine pills, although later on in his seaweed section he does recommend some that contain kelp: http://perfecthealthdiet.com/recommended-supplements/