Green chromis are actually just a variety of schooling damsels. They are social with their own kind, and do not show the same degree of territoriality, so some people separate them out mentally, I think. They do best in small schools of 4-6 individuals (lone individuals will sulk, and in pairs, the dominant may beat up on the other; keeping them in schools helps avoid this). Though they are small, they should be given a lot of swimming room. They prefer to school in the top regions of the tank. They are very hardy and have no other special requirements of any kind.