Thanks CMMorgan. It is sort of like playing Clue. It may just be the “silica free” aragonite is going to take a long time to deplete what it is not supposed to have. I wish I had identified what the 437 ppm were leaching out of the plastic barrels over the 3 years they were in use.I give you praise for your commitment to the tank. I had this issue in my first reef when I was running black sand. It almost ended me. Once I identified the problem and corrected, I knew it was worth the pain. You'll get there. You have experience, support and a desire to identify the issue. It's like solving a murder mystery... you just want to know who is holding the candlestick over the body. Please keep us in the loop... I'd love to know how your ICP comes back and your isolation testing goes.... following.