can anyone tell me whats the matter with my red tail catfish?

[bmwtwin2]

i took my red tail catfish out the tank on wednesday and noticed he had some red spots on his belly and reddness on the front of his mouth,
i took him out agin yesterday to check it again and it was even worse. he's not eating and it's starting to concern me what should i do to help him.
i had the water tested a few weeks ago and they said everything was fine but i didn't manage to get what the levels were i've, attached some pics of it. i'm not sure either wether i should treat it with melafix

 

[Lupin]

How big is the tank/pond?
How often do you feed?
What do you feed?
Temperature?
Filtration?
Any tank mates?

Please get yourself an API liquid test kit and check ammonia, nitrite, nitrate and pH again. Post the results here. In the meantime, do a large water change and do not use Melafix. Not really a fan of Melafix honestly and it is not a cure-all product. If the issue is related to water quality, Melafix will not do anything about it but pollute your water and suffocate the fish.