I am certainly no expert on metals, Randy is the expert on that but I think the problem it is way overrated. Especially things like hose clamps, iron and metal leaching from certain foods. I would assume some flake foods and prepared foods could have some metals but If it makes any difference to this discussion I have hose clamps, probably 4 of them in my tank for 40 years as well as 6 or 7 stainless steel screws, stainless steel ground probe and thermometer.
Not counting many screws, razor blades, needles and other things I have dropped and lost in there over the years. I also have been collecting water here in New York since the tank started in the 70s.
I don't keep too many SPS corals but I do have a lot of montipora and have had plenty of acro's until my clown gobi spawned all over them and killed them.
I think if metals were a problem, my tank would have more metal in it than a chain link fence or Schwarzenegger's biceps. I also don't use carbon or any other materials that would remove metals or change much water. Also, if you do any diving on steel ship wrecks you will notice many more corals growing on the wreck than the surrounding rock. I wonder why.
I just thought I would throw this in.