The first thing is to stop using Melafix. All the -fix products contain aromatic oils which can affect the labyrinth organ of labyrinth fish.
Next do a daily water change of at least 50% and see if the fin rot improves. You could try adding aquarium salt - 1 tablespoon per 5 gallons, completely dissolved in water before adding it to the tank. After a water change, add the amount of salt needed to treat the volume of new water. If this cures the fin rot, water changes without salt will remove the salt gradually.
And then yes, put a reminder on your phone and do a 50% water change every week