I have an update to this thread. Unfortunately Andy died today. He was a good fighter, but whatever was wrong with him was too much. He had been living on 2 or 3 live crabs a day, but had become very thin.
He stopped eating his crabs this weekend and his breathing had become really labored. I quickly filled my 55G (don't judge, that's all I have) as a HT. I put him in there last night and I dosed some CP (in case he had a parasite I couldn't see). He seemed settled last night and this morning, but passed during the day.
I still have no idea what was wrong with him. Whatever it was, he was the only one affected. I think it was a physical problem. He almost seemed like he couldn't swallow.
I was lacing his food with GC for a while in case he had an internal parasite, but that had no effect.
I will get another one, because I simply love them. I just don't want to repeat the same mistakes, if I indeed made a mistake. I even did an ICP test. I had low iodine, but I don't think that would cause this. It causes lockjaw in puffers, but he could chew fine.
Any other ideas??