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. If you have a protein skimmer you should shut it off when you are adding medicine to your aquarium. The protein skimmer will remove any medicines added to the aquarium.
3. 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.