I have had geraniums look like that when I let them dry out too much. I usually saturate them with water in the sink and let the excess water run through. My geraniums usually have small roots so it is easy to miss them with a half fast watering. Because of the discoloration, I would add some liquid fertilizer too. Usually I use 1/2 or 1/4 strength to avoid burns.
You have a lot of things on the surface of the pot also. Maybe that is affecting water distribution.
Other problems could be fungal but I don't think it looks like that yet. I would snap off the worst two leaves at the stem.
