I've got 4 sepia officianalis cuttles, a 900 gallon system. They were all doing fine yesterday, however one did not eat this morning, this afternoon he bagan holding his tentacles splayed out, then later his feeding tentacles began dangling and he died shortly. They have been here about 3-4 months and doing fine, however out of the blue a couple weeks ago, I had a nitrite spike, but was doing water changes almost every day. The nitrites yesterday were 0.169 and today were down to 0.158. Still not sure where the nitrites are coming from as they get water changes at least once a week regularly. When the nitrites spiked the water changes began every day or other day. They have all been acting normally despite high chems until today.....any ideas?