When a fish is stressed, it weakens the immune system allowing the fish to become susceptible to disease. Fin rot can come from poor water quality and-or it could be bacterial. Generally it is not severe enough to warrant full antibiotic treatment, clean water with the use of mild anti-bacterials, such as salt or melafix, will cure it.
You may stress your loaches more by moving them than by subjecting them to the meds..
