Simply Koi and More Koi

Any treatment needs to rub through your filter to be effective. It will knock your filter but it should recover quickly just don't feed much that is only my opinion

Hi doe you have the pump still for sale? I would be interested depending on how much you are looking for.

Regards

I usually heated to 13 but last year I followed advice from various forums and took it down to 9. I won't be doing it again as one or two fish were not happy with it and took a long time to perk up when raising the temps and were fairly weak coming out of winter and most had some indication of sligh...

Don't leave it alone - it will get worse. If it is surface damage then I would say clean, and treat with antibacterial solution. Others are far more expert so wait for more replies.