I dont use carbon except to remove medications. If you keep it, my suggestion would be to rinse it in old aquarium water just like your filter media (AFTER you do the filter media because of the carbon dust). You are correct that chlorine will kill the majority of the good bb in the bag, although it's unlikely to kill all the bacteria in the filter (but why take the chance?). Thats why I rinse in used aquarium water. If you want to use fresh water, many LFS
's sell RO
water for about 50 cents a gallon (bring your own bucket).
Carbon breaks down and eventually becomes useless. Opinions vary as to how long that takes but most that I have seen seem to think it to be in the 3 - 6 month range. After that, it acts almost like the bio rings and just gathers bacteria.
, unless you have medicated your tank and want to remove the residual meds, ditch the carbon. I use a synthetic floss that is used to stuff pillows in the last tray of my Fluval 305 to make sure I remove as much of the detrius as possible (It's cheap, comes in big bags at a sewing craft store and lasts for MONTHS). It also makes my water look sparkling clean.