Meds for fin rot [columnaris] are API furan 2 and Seachem Kannamycin. Both at same time .
I have those,
Metronidazole , Rid ich , praziquantel and clout on hand..
I don't count methylene blue , potassium permanganate or H202 as meds but have them on hand also. I do treat some issues with the MB and PP. The H2O2 is more for algae . PP is the most effect for broad applications but the hardest to use safely IMO
This link may help you find proper meds ...