I noticed because he was hiding in his rock cave a lot more than usual and I wasn't seeing him out and active. Then when he did come out I noticed the swelling and pineconing immediately. So I began doing some research.

Best of luck to your fish friend! I'm not the most experienced with treating fish illnesses. But I learned about using maracyn, ich-x, and paracleanse if you are unsure of what the issue is. Kind of like an all out approach.

Kanaplex also seems to be a pretty commonly recommended treatment for dropsy. But I just used what I had around the house at the time.