1. You should keep plenty of water testing kits for your aquarium. Testing kits can measure the levels of harmful and beneficial chemicals in the aquarium. You will need these testing kits for the frequent water changes for your aquarium.
2. It is not considered a good idea to keep aggressive fish with fish of other temperaments. You should keep peaceful fish in an aquarium with other peaceful fish to avoid any sort of fighting between the fish. Aggressive fish should only be kept with other aggressive fish.
3. After establishing your aquarium, pick fish that will add well to the current water conditions in your aquarium. Also be sure to check their temperament and other needs to be sure that they will make the transition in your aquarium smoothly.