While I have heard stories of success keeping multiple grammas, my experience is that they whittle down to at most two. I have tried getting a group of 6 twice, and both times after maybe 6-8 months I am left with 2. First time I got them from separate tanks at the LFS, second time I ordered them together, small size and told them not to let them be apart, but either way, they whittled down to 2. They always hung out together in the same part of the tank, but I suspect they kill each other off over time. I have a 210 with tons of rock and places for them to hide. I have been keeping fish for 42 years now, so not a newbie. Just wanted to tell you my experience.