i feel your pain, but I'm still very leary of trusting ICP. have you sent in a blank sample of just your saltwater? To a different lab? To a lab that uses a different method than ICP-OES? I know its an extra expense, but either there is a tin epidemic in reefing, or there is something related to the analytical method that is showing this as an issue. And as might guess, the primary provider of these tests has given you a reason to do more tests, and pay them more money to do so.
In my opinion, the probability of this being a biological issue or a nutrient issue is so much greater than the probability that one specific metal is causing you an issue.
Keep in mind most reefers (and most people) have no actual idea what they are talking about. I have two degrees in geoscience, with my graduate degree in geochemistry and a decade using analytical chemistry to solve problems with minerals and water. I am very qualified in this area. I am still only marginally know what I'm talking about.