Unicorn: good luck with the shelled pea treatment. You certainly seem to be doing your best for that fish. What sized tank is he/she in and how many other tankmates are there, by the way? Type of filtration and size/frequency of water changes would also be good to know.
One note: if it eventually comes to the point where you are considering euthanasia, flushing is most certainly not recommended. Not only is it an extremely painful way for the fish to go, but you could be releasing pathogens into nature.
One note: if it eventually comes to the point where you are considering euthanasia, flushing is most certainly not recommended. Not only is it an extremely painful way for the fish to go, but you could be releasing pathogens into nature.