I’ve personally never seen definitive copper toxicity - literally thousands of fish - yet home aquarists often have reports of this, why? One is I don’t use Cupramine that often. It has that detrimental reaction to reducing agents, I wonder if that trips people up? I do think Cupramine works faster than coppersafe - that implies to me that it is going to have more side effects. In any event, I don’t tell people not to use it, but if they ask what copper to use, I usually suggest coppersafe because it is more familiar to me.
Jay