My Star is about 12" in length and I have a 20g tank, but I do have 30+lbs of LR in there for him to hide and scavenge through. He has not bothered my scooter blenny but he has killed some of my snails and hermits. Actually he just took out one of my Olive Snail that I have had over 3 yrs. He trapped it in the corner of the LR and glass of the tank so the snail could not go anywhere and then chowed down for the next few hrs.