some 14 days ago I bought some new Corydoras (8 CW049 and 8 C. eversi). I had a good look at them before buying and am pretty sure that their barbels and fins were fine at that point. I drove them home in a rather big, open container with some activated charcoal added to the water, took me about 3 hours. I put them in a 54 L (cycled) quarantine tank after getting them used to my water and temperature. I didn't notice anything wrong with their barbels/fins back then although they were pretty stressed of course.
The next day I saw that a few Cories had missing barbels (only one eversi but several CW049) and one CW049 had almost his complete dorsal fin missing. They were behaving normally (not the typical new Cories swimming up and down the glasses) and were eating fine.
Since then I did daily water changes between 20 and 40% and added humic substances to the water. The one affected C. eversi has shown some regrowth in his barbels almost immediately but the CW049 are more or less the same, no improvement, no exacerbation. Is there anything else I can do for them? What can I do differently in the future to prevent this?
Edited to try to add some pictures. Sorry I didn't succeed.
Just came home from work and I think I see some barbel regrowth for the first time! I don't have high hopes for the poor guy missing most of the dorsal fin though. I would still appreciate any ideas how to possibly prevent this.