I have never had 2 blennies in the same tank...and had trouble keeping one in mine now (he/she carpet surfed). When I first posted on here you mentioned you had the same tank. Do you have a lid or anything retrofitted for the tank? Also, how is the tank going so far? I was thinking if I ever get one again, I need to create a lid for the tank, always loved the personalities of blennies. I would assume with enough rockwork, and if they arent too big you should have no issues. My concern would be one chasing the other to jump if there is no lid!