Thanks for that. This,
http://www.fish-helpline.co.uk/health/columnaris.html says it likes
cool water conditions and ours certainly does. We'll have a word with
the vet about antibiotics.

MediKoi is an antibotic food, if your fish are eating. TriCide Neo is a dip
that will take care of the problem if they're not.

You mentioned sediment in one post and that is where many bad bacterias
like to hang out, so I hope you removed as much as possible. A bad-bacteria
controller that we use here is called KoiZyme. See if you can find these
products in your area or a UK based internet pond shop.

Please let us know what happens. ~ jan


(Do you know where your water quality is?)