Its not essential but with harlequins it can be nice to try and keep the sizes as close to uniform as possible. The smaller the group the more likely that you may get a little dominance from a particular member or two. As you make the group larger, you will help make that harder and harder as there will be more distractions for the ones who might try to be a little more dominant than others.
Another thing to observe about harlequins is that they are sometimes seen now in a form that is a bit more pale pink than the traditional deep orange and darker pink. I don't think this is all about age, so its good to pay attention to. Harlequins will do great bringing properly sized quarantine groups in to join an earlier group in a main display tank.
~~waterdrop~~
