Thank you for all the information!
I will not give him any more salt, thank you!
I will get some photos in a minute!
I added a bit on the the message you quoted, he is breathing quite fast, is that to do with water quality?
Edit: What temp. should it be?
Breathing fast may just be stress, they do pant if freaked out, like after being chased with a net and caught, or if he's alone in a bare tank. Is the tank he's in now bare? What size is it and does it have a filter?
Temp - what temp is the main tank at? Panda cories should be kept at 72 to 77°F (22 to 25°C), refer to Seriously Fish for species information in future.