Problem with Gold Laser Cory

[seaweeds]

I bought 4 gold laser cory online and noticed this on one of my corydoras. I am new to aquarium hobby and have no idea what this is. It looks like cracks under the skin. After 2 weeks, I also noticed it on my other corydoras too but not as severe as this one on the same exact location. I searched online but could not find an answer. I have used ichx, api erythromycin, api general cure, and seachem polyguard but does not seem to heal. Does this have to do with temp because I am quarantining them at slightly higher temp. Does anyone know what's the problem with my corydoras?

 

[FranciscoB]

It will help to post additional pictures, different views, and to describe in detail what you are seeing that believe is abnormal or a problem. By all means, stop adding medicines and treatments unless you have a good diagnosis of the problem. In the single image shown, I don’t see anything wrong. Good luck!