Very difficult to tell if the fish are too damaged.
Typically the kind of damage caused by a PH burn would be more apparent by seeing cloudy eyes and labored "breathing" so you might be OK. If you are not seeing any other symptoms, other than lack of appetite, it may be a wait and see thing. The key thing here is that the fish were subjected to a high state of stress so in a weakened condition anything, including parasite attack, could be in play.
I would definitely not make anymore water adjustments since it is what it is now and parameters are all good. The impact of a PH change has already occurred so more change will just stress them out more.
If you can you may try doing a close up physical inspection of a specimen to see if you can see any issues with the gills or find any parasites (you will need a microscope for that).
Another thing I would recommend is to remove all the rocks that are inside the pond. Rocks look nice but create more problems than most people are willing to believe.
Last edited by Douwe; 3 Weeks Ago at 03:17 PM.
Thank you for all your help and advice. Very helpful. I will examine one.
Post good pics if you can.