Poor Fish

It has now gone a week since we bought the little baby koi. Sadly, Tango and Custard dind't make it. I couldn't actually see anything wrong with them but they still died. Tango went first and it made feel sad because it seemed a bit bigger than the others so I assumed it was quite strong, then a couple of days later Custard died too and since then I barely dare to look in the tank in case there are more. I am dreading getting fin rot again and lose them all. However, this morning, Bluey seemed fine. Fingers crossed that he makes it.