Hi. I am looking for information about something I read about called a "chain tensioner". The chain on my 3+ year old bike is loose and keeps slipping off. Dangerous! Apparently a tool called a chain tensioner can simply fix this problem without taking the thing to a mechanic. I want to learn how to do this but a search for chain tensioners returned dozens of different looking tools, and I don't just want to buy one and hope it's the right kind. Any suggestions as to my next step?
Thanks in advance