Ever the stubborn aquarist, I bought another octopus, my third. This one seemed promising; I got him from my LFS, and he was happily exploring the tank after acclimation. Then, suddenly, he jerked as if something stung him. All his legs extended fully, and he flipped onto his back, furiously spraying ink. He seems to be currently in a state of semi-paralysis, with his legs still extended and only partially responsive to his attempts to move them. He is breathing at the moment, but it doesn't look good, to say the least. I believe I caught the event on video, as well, though I'm unsure since my batteries were low and cut off around that time. I will try and upload the video after it charges. The only thing visible around him were some pieces of dried coral. All water conditions were fine, from the last time I tested a few days ago. What could possibly have caused this?