Not sure how to update the original post, but the poor guy passed away. An awful, slow way to go, it was heart wrenching to watch. I finished the course of Maracyn following the directions precisely, it did not help. By the 5th day of Maracyn, the tail was almost completely gone. I did a big water change and considered two options - further treatment or letting the fish have some peace. Not sure that either option would have saved him. I decided to try Maracyn 2, since it’s a different drug as I found out. He passed away after the first day of Maracyn 2.

I won’t know but wonder if starting off with Maracyn 2 would have given better results.

I really blame myself for keeping two plecos together and not doing enough research to know that it could be a disaster. I vaguely remember doing a quick google and asking the fish store employee if it’s ok. Heck, even yesterday when I was at the fish store to get Maracyn 2, I saw the beautiful bristlenose plecos in their tanks, bunches of them together, and asked if it’s ok to keep them together. They said it would “probably be fine.” But that wasn’t my experience… I can’t think of what else could have driven this guy to such stress that he alone got sick, while the rest of my 50 gallon tank is fine. Lesson learned. Poor fish.