make sure engine is idling at proper speed also
should be around:
GM V6: 625-675rpm
Diesel: 725-775rpm
once confirmed and alternator still not charging at idle THEN you can check belt tension and tighten as needed.
Pay close attention to pulley on alternator and condition of belt, if belt is worn or pulley on alternator is worn it could slip and cause this issue.
good luck
This is ONLY to be used to report flooding, spam, advertising and problematic (harassing, abusive or crude) posts.