Update: Spot Cleaned his tank this afternoon (he already peed, so I got rid of the urates and added some fresh substrate). He showed no aggression. Didn't hiss at me, defensive strike, or anything. He did poke his head out in curiosity to see what I was doing, but that was the extent of it. He did curl up into a ball when I removed his water dish (it's attached to his hide) but there was no aggression again. He does look super cute though!