1. When adding particularly aggressive fish to your aquarium, it is a good idea to move around the rocks and such in the aquarium before placing the new fish into the aquarium. Moving the rocks in the aquarium will allow the fish to go back and stake out their own territory.
2. Angelfish are normally very peaceful fish, in times of breeding they can get aggressive. It is a good idea to only keep one pair of mating angelfish in the same aquarium, as more of them can lead to infighting.
3. When starting out a new aquarium, it is best to add hardier species at first. Once your aquarium ages a bit and gets settled, you can start to add more sensitive fish to the aquarium.