Well, where should I begin? Our octo hadn't been seen in 3 days except a possible sighting when the lights were out in the afternoon on my webcam. My fiance thought he was dead and wanted me to fish him out from under the rock. I suggested running some water tests to see if he was dead or not (I figured I would see it in the water test). She insisted, so I moved the main rock that he hides under. He was sitting there half buried in the sand, not moving. I poked him a bit and he appeared to move. I grabbed a turkey baster and gradually blew most of the sand off of him. Once he was completely uncovered he let out a huge blast of ink and shot off into the corner of the tank. I replaced the rock (I couldn't get it the way it used to be, so his old home is ruined) and we immediately did a 25% water change. I also put fresh carbon, silicate, phosphate and nitrate sponge media in my canister. The water was still a bit dark so we did another 25% water change. Now the tank is still dark (has hasn't inked again). I am wondering how long I should wait to do my next water change? I don't want him to sit in the ink too long. It isn't cloudy, but it is obviously a bit darker than usual. I am hoping that the carbon will pull most of it out by tomorrow. A few questions.... Do you think he is sick or something? He used to come out every day to eat and now he hides all day. How long do you go without seeing your octopus before you start thinking that it may have died? What should I do next? I have a perfectly clean reef tank that I can use for a water change if it will be any better than freshly mixed saltwater. For example, I can take water out of the reef to do a change with the octopus tank, and then use freshly made water to fill up the reef. I don't know if this is any better than new water. My reef tank is perfectly clean, no nitrates/nitrites/ammonia. Any advice at this stage would be VERY appreciated. I'm not sure what to do next. My reef tank experience normally makes me inclined to do nothing and have patience, but it hasn't paid off with the last 2 octos, so I can use some advice. Thanks!