All very good comments.  I ...

All very good comments.  I just want to support the comment from Soloman and others who mentioned pH.  Corrosion can be due to biofilms, but also due to an unstable water.  Adding chlorine tends to consume alkalinity, and if your water is already unstable as measured by e.g. LSI, it will become even more corrosive after chlorination.  Using a programme such as STASOFT made freely available by the South African Water Research Commission you can easily assess the stability and determine what to do to make it stable.