If you know your fish list well, you can let the shy and slow eaters to go in first. Let them get used to the feeding habits and hiding grounds. Small fishes can be aggressive too such as damsels and Chromis. My 2 inch queens angel is bullying my 6 inch soldier fish in the qt! Certain species have very low tolerance to others of the same type, even if they have the same size. For example, if u want to have multiple tangs if the tank is small, add all of them together if possible. It will divide out the aggression. Just my humble opinion Sent from Singapore Reef Club mobile app