18.5 Weeks and I am seeing some aggression between some of the cuttles. As a result, I had to remove a cuttle tonight and put it back into the 20G long rearing tank.
Yesterday, I noticed that one of the cuttles had a white mark on the end of its mantle and it was covered in circles made by thin white outlines on its skin (see pic below -- it's the best I could do for now). I will call him "Chafe" and assume he is a male although I don't know that. Chafe was also reluctant to feed yesterday. Today, Chafe ate OK, but I woke up in the middle of the night in order to observe what was going on when the cuttles were active at night.
Tonight, Chafe was solo floating around in the tank near the top of the water column. As he made his was down towards another cuttle burried in the sand (the burried cuttle was displaying mainly white colors to blend into the substrate so I will call her - another assumption - "Milky"). As Chafe got close to Milky, a large cuttle (aka "Brutus") came quickly from a nearby rock, displaying very dark (looked black under the red lights) colors and flashed spots and stripes. He then proceeded to attack Chafe and would not let go. Brutus dragged Chafed around the tank and while Chafed broke away a couple of times, Brutus came back at him.
Fortunately, it was not difficult to remove Chafe. He was too nervous to go down, so I was able to scoop him into a plastic container and move him to the 20G Long in the fish room (this tank is plumped into the same system as the display tank). My hope is that he will heal and be OK in this smaller tank until I can find him a home, but I don't know what type of healing cuttles do.