IMO/E....the very best medication/treatment for our freshwater fish is......fresh, like temp, dechlorinated water....along with good/proper nutrition that supports the fish natural immune response and antibody development.....
Sometimes/often-the OTC products/medication/chemicals/pesticides sold/used can do more harm than good...especially when you don't know what you are treating.....you can risk: overdose and the fish become toxic, killing the good bacteria/pathogens (
not all pathogens are pathogenic) destroying/hindering antibody development, compromise the immune response to name a few.....
Prevention and support of the fish natural immune response by providing proper care with good husbandry practices, proper nutrition...etc.....
The balance of enough water changes to maintain water quality but not so many that you destroy/compromise antibody development....in other words....the tank can be too clean....its hard to support life in too sterile environment....
And don't forget the importance of proper acclimation with new fish and 100% water changes......tolerance can very due to many different factors and sudden chemistry and temp changes can be stressful and that stress can compromise immune response.....
Then patience.......everything takes time......