Try feeding some peas, skin and blanch the peas first. What are your water parameters? Epsom salts can be helpful with swim bladder troubles although I will research whether or not they will harm cories for you. Regular salt will harm cories and I am not sure if epsom salt will. I will check and post back. You could do a pwc
for starters. What size tank?Are there any injuries to the fish that you can see?