Chromis:  Notes From Penny:  Blue Green Chromis are the only fish in the Damsel family that I find is truly reef safe.  It is never aggressive & is considered to be a cleaner fish (meaning it will pick parasites off other fish).  Other Damsel species have a super territorial nature & will bully newcomer fish.  Some become very large & aggressive with all tankmates!  Try getting a Damsel out of a reef tank.  NOT fun!