I have a 20 gallon acclimated tank with barbs. I recently began planting the tank which is going quite well. However, while doing a routine water change yesterday I used the metal from twist ties, the regular household kind, to bunch some plants that wouldn't stay put. All barbs were healthy and active. Water change as usual, 25%, from buckets with temp controlled and water conditioner added before to dissolve. This morning and through the day, four of the barbs died suddenly. I thought it was somehow shock. No disease on bodies or alive fish. The last one that died had bleeding from its stomach or anus. I tested water and all is good. i thought about the metal and cannot find anything on a web search related to toxicity. I of course removed these plants and the metal and did another 30-40% water change. any suggestions here? Is this toxicity psooible? If so, what can I do?