[KoiCop]

Hello Isis . . .

I tend to agree with Graham that you've picked up a parasite problem -- possibly by intoducing fish without sufficient quarrantine?

How long ago were the newest koi added?

What is your water temperature? Sometimes that helps to identify what type of parasite might be involved. With the symptoms you described and cold water, for instance, costia readily comes to mind and chilo can't be ruled out.

Please update your profile to let us know where you live, OK? It not only will help us to understand your pond dynamics, it helps when making referrals to knowledgeable ponders in your area.

Since you're using metric units I'm going to assume you're not in the US?