I don't really think its stress, the Oscar behaves and eat normally, he shares the tank with 2 smaller parrot fish, he gets along rather well with them and i have only seen it chase one of them once.
I do a 25 % water change weekly or so, the tank is near a window so algae does grow, however removed quickly using a magnetic scrub. (water looks slightly greenish because the lights in fish tank are off and when taking the pic the lights in the room were off too, as only sunlight was lighting the room at the time)
I have seen some of the small bumps on his head such as the one above his eye in the last pic for some time, however the larger white cut/hole appeared 1 day ago.
i will take more pics later, I am not at home
the tank is 55 gallons btw