Hi guys- thanks so much for giving me your advice on this. Yes, right now he's about 4" long. He is very active at night too, which is really cool. Ummm, I ran across a way online to teach a knife to come out and eat from the palm of your hand whenever you put it in water. I'm going to try to do that.
Also, the knife is in a tank with a blue crayfish of similar size. The knife made it thru the first night, but long term would it be wise to keep the lobster in the tank, with his sturdy pincers always looking for a victim? I'm sure I would have to remove the cray when the knife gets big, but for now, they seem to get along OK... As always, I appreciate the feedback and advice on this new fish.
Thanks!