I am having a similar issue. I had 10 in the big tank and 2 are much smaller. During feedings the others would actually grab at the 2 lil guys who fled to the top and are not getting much larger! I took them out and put them in with Baby, Hoppy and Shadoobie where they seem much happier and closer to their size. Maybe it's better to separate them, just in case. I was under the impression that Gray's were not aggressive, but it sure looks like they can be a lil when food is concerned and it shows in their actions and slower growth! If Big Mama is intimidating them and they're not eating as much or without BM menacing, why take the chance. I am only basing it on what you've said and my experience so take it with a grain of salt!LOL I am not an expert, but it's just an observation Best of luck and enjoy your vacation, boy am I jealous!LOL