Melafix is great stuff, but if you've got severe fin and tail rot, you need an antibiotic. Melafix is more for frayed fins or fins damaged in a fight. It's great if you have fish that have rubbed or scraped against a sharp object, and also great if you're trying to heal a fish after successfully treating for a parasite or fungus. Although I know from experience that fins really just need clean, warm water to re-grow after injury, I do use tea tree in my tanks to aid in the process. You can save a lot of money by using tea tree essential oil instead of the commercially prepared Melafix. I've heard different people give different dosages; I have been filling a small water bottle with tank water and dropping the essential oil in, capping it, shaking it, and pouring it into the tank at approximately one drop per 3 gallons of tank water.