How to proceed in case of a repeated treatment with sera mycopur?

I am currently treating a fungal infection on an angelfish in my 240 liter aquarium. The fin base of a pectoral fin is affected. I use sera mycopur in combination with sera ectopur. Concerning the application, the sera mycopur package says to treat for 3 days with the given dosage of 1 ml per each 20 liters. How do I continue the treatment if the infection is still present?