Betta with scratches and ulcer

HI everyone! I have had betta for years and currently this is the first time I have experienced this type of illness/injury with a betta. He looks like he has scratches on his body and looks like some sores/ulcers. I did some research and have been using Furan 2 for the last several days but still am conferenced. He shares a 10 gallon tank with another betta but it has a divider that goes all the way up/down so there is no way that the two got together and there are no other fish in the tank. Any ideas on what this is or ways to help treat it would be appreciated.

 

Is there anything in the tank he could be scraping himself on?

 

The only decoration in the tank is a plant

 

it could be a fungal infection

 

After the antibiotic I was going to go through a fungal treatment as well.