Merlin is dead, and I feel like I killed him.
I've mostly tried to leave him alone since he very recently began slowing down with age, but his water was getting filthy, and all the partial changes in the world weren't going to change that. I did a 100% change. I really, truly felt like he would feel better if I did, but I guess the shock was too much for his system.
Thanks, 1fish2fish, for giving him to me. He was a great little guy and I'm really going to miss him. It sounds horrible, but I'm glad he's gone. It hurt to see him so sick.
I'll go bury him later.