You will need to treat the fish for several weeks or until it looks better. However, if there has been no improvement after 2 weeks of medication, then it isn't working and you need something else. But give the fish a few weeks without medication before you try a different medication.
Malachite Green and other medications need to be added regularly. Follow the directions on the packaging. Wipe the inside of the bucket down and replace all the water before you add another dose of medication.