After exhaustive googling over his problems (emaciation and a hollow body, paleness, lethargy, swim bladder) I decided to treat him with kanaplex. He got his first dose 48 hours ago and he was already flaring at the back tank wall last night. This morning he's cruising around and flaring. I'm going to do a big water change and redose him. I think I'll go with three full doses just to be thorough. He still can't swim to the bottom at all. I'm hoping he's not permanently damaged but he's tough and strong. I have him on frozen bloodworms only right now.