what does the chloramine do to the carbon?
It oxidizes the GAC carbon surface, giving CO* and converts the Chloramine to Cl- and Ammonia by reduction. Some of the oxidized GAC remains and some of it breaks down to O2 gas. It will not shorten the life of the GAC from a rinse. The life of GAC is lost in a RO/DI unit because the water with chloroamines is continuously going threw it, day after day, week after week and month after month. Any ammonia or Cl- in the GAC from a rinse will be little and hurt nothing. You are talking much less than 1 % lost from a rinse. For as soon as seawater passe thorough it will be rinsed out. GAC does not bind Cl- or Ammonia. The Cl- leaves the GAC and is taken out by the RO and the Ammonia leaves the GAC , goes through the RO for the most part and is taken out by the DI, not the GAC. So, if one is worried about this just do a final rinse in RO/DI. If you want to rinse it in RO or RO/DI or seawater fine. I raised my GAC in tap for 35 years. Why ? It was just so much more convenient and back in those days there was no such thing as RI/DO. If I was starting over, the same, tap water rinse.