That mister I found at a yard sale nearly killed my whole rack
Picked up a vintage brass spray bottle for $3 in Eugene and thought it was a score. Turned out it had leftover copper residue inside that leached into the water every time I used it. My ferns started browning within a week and I spent a month adjusting light and soil before I checked the damn mister itself. A quick vinegar soak fixed it but I lost two nice Boston ferns in the process. Anyone else ever get burned by secondhand watering gear or old pots with mystery stains?
Figure out if you're sure it was the copper and not something else like overwatering or a light change. Plants brown for about a hundred reasons, and blaming the $3 mister is the easiest one to point at. Even if there was residue in there, a quick rinse would've handled it before it did real damage. I've got old sprayers with god knows what in them and my plants are fine because I don't let them sit with stale water. You probably just had two sick ferns already and the timing lined up.