Melafix will do an adequate job on a lot of things but it is not the best thing for finrot. Raising the temperature and giving something like Maracyn or the Jungle Labs Fungus Tabs (they fizz in the water) It is also (like J-Man and Butterfly said absolutely necessary to keep the water clean as it is caused a lot of time by poor water quality)
I am very sorry about your fish. It is so hard to lose a fish at any time and when they are sick it is a real worry to know what to do to help them. They are just like a part of the family. My deepest sympathies go to you and I have respect for you for caring so much for your fish. Bless you.
Sorry about your fish, I feel for you, I know how it feels. I would just keep doing water changes and don't mess around with the tank at all, like changing stuff around and adding chemicals (accept antibiotics or something to help them) and new plants and fish for a month so the new fish don't get it and your tank settles down. I found that this is the best thing to do.