Epsom is OK for long term use. It's aquarium salt that can cause damage if used for too long.
I wonder what his problem is as maracyn shouldn't work on columnaris because columnaris is a gram negative bacteria. Maracyn fights gram positive bacteria.
Maracyn
Active ingredients: Erythromycin
Diseases: gram positive bacterial infections, fin and tail rot, popeye, body fungus
Comments:
These antibiotics prevent protein synthesis and effect the cells ability to reproduce.
Further information can be found under the name
Erythromycin.
Erythromycin
Diseases: bacterial infections, intestinal flagellates
Contraindications:
It was noted to be quite effective when the pH is neutral or slightly alkaline.