At least I can measure the difference when I dose iodine.
I was reluctant to buy a iodine test as I was thinking that it would be too hard to measure home concentrations as low as those present in natural seawater. The test has shown zero iodine in any form in my fish tank, but soon after I started dosing iodine daily I was able to detect it with the kit. I am not sure how accurate it is, but at least it is better than nothing. An ICP test would provide a more accurate data and it would be interesting to compare the results with this test kit, but unfortunately I have no access to ICP testing yet.