In the case of injury and popeye you really dont need meds (but always good to have on hand just in case of bacterial causes)-it should clear on its own given water changes.
i know how you feel. Once had a similar situation and now dont use divided tanks. His injuries should heal up just fine. When it happened to me one of them had more than half his tail gone and in a few months you would never have known there was in issue.
best of luck-sorry about your divider woes.
cheers