Shell soft and exposed bone

Hello!
Looking to see if anyone has any ideas what’s going on with my RES. I was examining him today and noticed he had a bit of exposed bone and there’s a part that looks like it’s just slightly softer than the rest of the shell and it’s mostly in the joint area (I circled it in the photo). I immediately started dry docking him and applied silver sulfadiazine in case it was shell rot
Any idea what’s going on and how to treat him??
Looking to see if anyone has any ideas what’s going on with my RES. I was examining him today and noticed he had a bit of exposed bone and there’s a part that looks like it’s just slightly softer than the rest of the shell and it’s mostly in the joint area (I circled it in the photo). I immediately started dry docking him and applied silver sulfadiazine in case it was shell rot
Any idea what’s going on and how to treat him??