1. You must always treat the water in the aquarium before attempting to place fish. If you fail to treat the water the fish can die from the condition of the water.
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. You need to have some healthy natural bacteria to process the wastes and chemicals in your aquarium. This will take around 4 weeks to grow naturally, but you can purchase products to speed up the process.