just because the fish you stock swim off does not mean they will live. I think your dead grass carp must have been a bit stressed and it took some time for him to kick.
I treat ponds after stocking grass carp most of the time. the carp will be fine, they slow down and dont eat as much after the treatment. they wont die. you will need to treat the weeds to gain control this year, then next year your carp should handle things, if not consider stocking more and make sure to haul them properly and temper them with pond water before stocking
