Any idea what this reaction is? I put 4tbsp of sodium metabisulfite in a gallon of water and put it in a 10 gallon brute, along with some things I wanted to disinfect. All plastic or glass. I didn’t have a lid for it, so I put this large stainless steel bowl over it. Came back a few days later to this rusty goo all over the bottom of it. It doesn’t rinse off, but I managed to scrub it off with a brush, but it’s left behind black bumps that I haven’t got off yet.