[Graham]

Quote: Originally Posted by Isis The newest koi was added two weeks ago and died on saturday, live in south africa, mid summer here now - not all the koi are battling. The water temp is about 17 degrees celsius.

Pretty safe bet that you've got a parasite problem....and the water is a minor problem. Can you contact someone from the SA koi club. They'll be able to do a scrape and scope for you, so you can ID the bug. Try contacting Dr Jim Phillps at Welcome to the Official website of the South African Koi Keepers Association - koi, nishikigoi, japan, showa, sanke, kohaku, shows, sakks, koisa magazine



If not then look at shotgunning the pond with something like Formalin & Malachite Green.