Looking at video l think it swin bladder I would qt and not feed for a couple days add aquarium salt 1 table spoon for 2gallons for 5day if salt does not work try maracyn swim bladder can be caused by a bacterial infection
I would treat for the fin rot with maracyn panda Cory's like a temp between 72-77 when treating with meds you only have to remove actived carbon pad you can leave other pads in filter
I feed a mixture of Hikari micro pellets and wafers Vibra bites and bug bites and frozen or hikari bio encapsulated freeze dried for I find feeding a variety of foods produces stronger healthy fish
I would treat for bacterial and fungal infection to cover all bases good disease book recommendation Gerald bassleer the new illustrated guide to fish diseases