1. When keeping aggressive species of fish, it is best not to introduce peaceful species of fish among them. Aggressive fish will tend to bully the more peaceful fish. Make sure to thoroughly read about the compatibility of the selected fish for the aquarium.
2. When adding new species to your aquarium, you have to ease them in. Adding too many fish too quickly can cause the ammonia and chemical levels to raise quickly. Adding fish slowly gives your filter time to catch up.
3. Research the aquarium equipment you are looking at before you purchase it. Different sizes of aquariums require different pumps and heaters. Find out which products are best for your aquarium before you start ordering the wrong products.