thats really only unless you really concentrate the water in salt, which on it's own will kill the fish. Normal doses of salt as done here where it's 1,2,3kg's per 1000 litres does not have that great an effect on zeolite. It has to be a serious concentrate of salt to release the ammonia from the zeolite.
Chris Neaves told me this the other day. When my yondan kohaku was lying on it's side I was worried to add salt when told to, but was advised on the above that unless it's a serious concentrated solution and is soaked in this solution that only then will the ammonia release, which the solution itself will probably kill the koi.