My guess is that it is a "common" pleco, Pterygoplichthys joselimaianus or
Pterygoplichthys pardalis (from the shape, I would guess more joselimaianus than paradalis). Though the color looks more like a chocolate or rhino pleco, Pterygoplichthys scrophus (I can't tell if there are "horns" in the picture). However, I think it's lighter in color because it's stressed out and/or it's trying to blend in with the white gravel. I would suggest getting some more hiding places for it, and if possible changing to a darker more natural gravel color.