I have been researching all the cuttle articles I can find (TONMO, the ceph page, goggle) and can't find anyone recommending calcium. I was thinking how does the cuttlebone grow without calcium added? I understand why octos wouldn't need it, but that cuttlebone has to grow awfully large-awfully fast. Could that be a limiting factor in the raising and breeding of cuttlefish? I noticed in some of Colin's photos he had corals, did they receive additives? I also noticed that the brand name "Fuji Mud" is talking about the calcium and minerals in mud patched just outside the reef systems. http://www.marinedepot.com/md_viewItem.asp?idproduct=WS1111 http://www.marinedepot.com/aquarium_additives_walt_smith_fiji_mud_gold.asp?CartId= This is also where cephs like cuttles and muck animals mostly live. Could they need these conditions to thrive? Unless anyone can give me a reason not to do this, I am going to try supplementing my tank as if I was stocked with stony coral. I will be learning how to track absorption of calcium, so I can see if it is actually being used.