Since you don't know exactly what it is, I would continue trying the treatment you are using to see if that helps, but I personally would try water changing about 50% each day or every other day since clean water can be a huge helping factor with disease. Like I said, the pics are a little hard to see, but it looks like he may have a little fin rot going on, which is helped by keeping the water pristine. I wish I knew more about what it was. I am not great with disease diagnosis, but for now I would continue with that treatment and do water changes. If that doesnt help, maybe try and get a more specific diagnosis so that you can treat the specific illness. Good Luck.