Kelp varies in Iodine content as well as mineral content dependent upon the source. many things get passed off as kelp that may be considered a "wrack"...
A tablespoonful of most Norwegian kelp usually will have about 5.8mg of iodine... I take between one and 2 tablespoonful a day now and had, up until my Iodine supplementation with Lugol's taken 3 tablespoonfuls a day for a long time with excellent results.
I also take chlorella and spirulina daily.
Been doing this for over 2 years now... that in addition to eating dried kelp as a snack most every day and a tablespoonful or 2 of dulse flakes I use in food prep daily as well.