Don't worry about iodine. Neither OES nor MS can tell which type of idoine was in the water and only Iodide is useful... Organic Iodine, elemental iodine, iodide, iodate, I++, shineola, etc. and all of the other forms show the same peak on ICP, but they are not useful. The compound matters, not the element, which is true of most things which is why ICP often has more questions than answers. My point is that it is not likely that iodine is overdosed, just in a form that is measured but not active.
If you are feeding your fish a wide variety of food, and enough of it, there are likely enough traces in it to supplement something like a CaRx or other way to get the macro elements. This includes iodide. Most of those elements do not have a known useful set point in marine aquaria that people other than supplement sellers can agree upon.
There are some massive ICP and trace threads on r2r with the organic chemists like Bingman, Dr RHF, including Cristoph who owns Oceamo, that outline what you really need to be looking for. Most things that come back in a test that are useful are done with titration, conductivity and stuff and not so much the ICP. A definate rabbit-hole, but a good read. In the end, you end up questioning everything that anybody knows about anything beyond probably 6 parameters.