1. It is a good idea to keep carbon on hand in case of emergencies. Carbon can be used to soak up anything harmful that may be introduced into your aquarium. So keeping an emergency stock can be a life saver.
2. 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.
3. Provide plenty of places for your aquarium animals to hide. Studies have actually shown that the more places a fish has to hide, the less likely they are to do so! Hiding spots also provide safe spots of refuge for smaller fish in the aquarium