Is this some sort of infection?

[AR1]

Have you tested your water?

No

If I did not test my water...

...I recognize that I will likely be asked to do a test, and that water tests are critical for solving freshwater health problems.

Do you do water changes?

Yes

If I do not change my water...

...I recognize that I will likely be recommended to do a water change, and water changes are critical for preventing future freshwater health problems.

Seems like a injury from scraping itself against something hard but not sure.
kno4te

 

[danotaylor]

Pleco injury perhaps You could catch it and dab some betadine or methylene blue directly into the open areas. I’d add salt to the water as well mate. 1tbsp/5gal