We have two in our high school tank, but it is 220 gallons and there is plenty of live rock (about 300 lbs) The scooter blenny's roam around the tank picking up loose food on the rocks and the sand. They are slow eaters, but continually forage all day. They have gotten bigger since they were introducted to the tank about four months ago. The mandarins are also very picky in what they eat. I raised copapods and gave the the young nopillae from that hatching as well as a bit of mysis shrimp that they would pick at. They are slow eaters and hard to keep unless the tank is really establsihed. Both Carolina Biological or Conn valley biological sell copapod starter kits where you can grow them in a two liter bottle. This is a bit tedious, but we wanted them to be well fed.