Thing is potassium permanganate is the witch oil some aquarist like to use these days. It’s a cure all exlixir for all fish ills. Nope! But yes it’s was probably a cross contamination. 2 weeks in qt isn’t long enough. 4 weeks qt than add your least liked first discus and add to the new discus tank. Have some rid-ich plus available if there’s a problem. This usually works on cleaning up whatever the older discus gave the new ones. Once all is well add to the old discus tank.