This happened to me at my high school graduation. My 3 year old cousin threw a handful of pennies into the refugium on my 187 gallon. I ended up losing my urchin, my snails, my cleaner shrimp, my bubbletip anemone, and all the caulerpa in the fuge. Surprisingly none of the hermit crabs seemed to be affected.
I only figured out why everything was dying when I was pulling out masses of dying caulerpa and saw a penny. With more searching, one penny turned into 18 pennies.