I feel your pain! I have exactly the luck you do
I am a reefer, but I also have a passion for Koi, and my 3000g Koi pond is my baby... They are wintering outside as they do every year, and the winter is so close to being over! But of course, I found my prized japanese $250 imported Matsuba Koi belly up the other morning with NO explanation... the ONLY koi death I've ever had during wintering, and it had to be my imported baby!!! GAHHHH!!! WHY!