I have some young blue acara at the moment from 1" - about 3" they are the first ones I have kept and I think they are absolutely great, they are really cheeky and always at the front of the tank (very greedy too) I have 4 larger ones (about 4")in my main tank with 2 serverums, a firemouth, an elliotti and a rtbs the acara are very quiet and tend to stay together, they do chase each other occasionally, but no fin nipping or nastyness.