Boy he sure is a fighter! I hope he pulls thru Diana.
Well, crud. Came in this morning and he was gone. The water may have gotten too hot - it was up almost to 90 (I guess shallow water would get warmer), but I could now see the area where the blister had been, and there was a large red area inside, so I suspect a tumor more than anything else.
I'll try to find a photo of him to post - he was hard to get a photo of because he would run away when I got too close - until this happened and I removed all the plants and stuff from his tank (just leaving his rock, which he used to prop himself up).