Has anybody had issues with using Granular Ferric Oxide or Iron Hydroxide with cephs, specifically cuttles? I bought some PURA Phoslock last night and added it per directions for an established system trying to lower phosphates. I added approximately 6 TBS in a mesh bag which I rinsed thoroughly. I also added 2/3c of carbon which I haven't put in for several months. Parameters yesterday: NH3 0-0.1 NO2 .1-.3 NO3 5-10 pH 7.9 PO4 2.5 I came home this afternoon around 2 and found one corner of my tank covered in ink. I saw one cuttle in that area with extremely dilated eyes spurting bursts of ink every few seconds. The other 4 cuttles are acting normal. I changed some water, and tried to feed the stressed cuttle, who was disoriented and barely moving. I got no response from the cuttle. The intake tube from my Fluval 405 had the cuttle lightly pressed against against it. I moved it around with my hand, and put it near the glass to examine further. The cuttle's proboscis were uncurled and limp. The cuttle's skirt was no longer moving and it had turned completely white. If I squeeze the belly of the cuttle, it is soft and full of ink. The ink exits out of the cuttle's siphon which leads me to think of the possibility that it was suffocated by the ink. The only thing I can link the death to is my adding of the GFO last night. I took out the bag of GFO for now. I also set my skimmer to skim wet, and left the carbon in. Please let me know if anybody else has noticed any behavioral differences with the addition of GFO so we can find out if it is bad for cephs or not. It is possible that there is another solution to this death however I cannot think of anything at the moment. I have pictures I will post later of both the cuttle that died and the the others. I also have a video I will try to post if I can get it small enough and retain quality. Sad thing is this was my mature female. I have one other female (a runt - still a lot smaller than the others) which I began to see breeding with my males a week or so ago, so there is hope that she will still be able to produce fertile eggs.