Why does my Cory catfish look like this?

[RainGamma]

I agree, what are your ammonia readings? They should be at 0ppm.

Forgot to add that, it’s 0

 

[Barry Tetra]

Next time when you buy fish put them in the quarantine tank first.

 

[utahfish]

Sorry bout your fish, that sucks.

 

[PheonixKingZ]

If your Ammonia reading is 0ppm, then its not Ammonia burns. I honestly don't know what it is.