The position of that mark makes me wonder if it's actually an injury, and not an ulcer. It looks too clean and there is no red area around it.
I've had a similar sort of injury happen to one of my fish, when it dashed madly thru the tank, after a fright, and hit his head on the bracing at the top of the tank.
Keep an eye on the injury, and if you notice it starting to get worse, or if you see any reddening around the edges of the injury, please let us know.
If it's just an injury, it will begin to heal very quickly. Daily water changes will keep the water clean and the bacteria count low, which will aid in healing.
Thirty-five years keeping and breeding discus, and I'm still learning :P
I think it is injury too. The "skin abrasion" does not look infected to me either. The discus has remained very active and always looks for food. I will do 30% daily water change for a few days. How long will it take for the lesion to heal up? Would add in salt facilitate healing? I am using Aqua plus by Hagen to condition my water and it claims that it will protect skin and speed healing...is this true?
talking about salt can you use it in a barebottom tank with otto, bristlenose catfish, neons and rams also an angel just asking because i want to give the discus a salt bath.
Also is it a good idea to give a salt bath once while for discus(same tank as above)