Hi Susan, carp pox looks like waxy small lumps not a "dusting" as you describe (?). Carp pox usually disappears as water temps rise and the koi's immune system operates more effectively (at 8 degrees a koi's immune system is pretty well switched off). Do a "Google" search for carp pox and you'll find lots of pictures to help you in your diagnosis.
My guess is that your problem could be one of these two protozoan parasites; costia or white spot. But without a microscopical examination of a mucous sample it is very difficult to be 100% sure about a diagnosis. Can you get some help from a local hobbyist, koi club or koi dealer ?
Good luck.
Posted on Mar 17, 2006, 10:03 AM from IP address 81.132.25.202