I just put the cuttlebone into the water, it floats for awhile and then sinks. I have also used eggshell, I have tried breaking it into small pieces and I have also used a mortar to grind them up into powder. Some break the shells up and put them in a net and hang them in the tank, I just mixed them with the substrate. Also depending on how big your tank is you might want to get more than one cuttlebone, since the calcium disolves into the water I don't think one bone is gonna do much good in a e.g 20G tank.