Tension pully

Maybe the spring is broken on the tensioner, you can test by putting socket on the bolt that holds the pully on. Maybe a 14 or 15 mm socket. With a breaker bar see if it turns easy or has some strengh. If it is easy your tensiioner is probably bad. If it is hard it's probably good. The belts some time streach depending on the grade of belt your are using. But to answer you question, you should not require any special tools.
Hope this helps.
Good luck