Nothing solves the problem forever, only for a while. Tensioner will continue to need adjusting or replacing as well as the belt. As I've said before I have friends who are on there 4th and 5th belt and counting, I am on my third.
Should run you around $100 parts and labor to replace the belt.
BTW, I didn't want to do it but for those of you that used belt dressing and things just got worse, I TOLD YOU SO.