1. You should take out any carbon filters in the aquarium when you are medicating your fish. The carbon in the filter will remove the medicine from the water, so it is best to remove it all together.
2. It is generally recommended to use natural gravel for the aquarium. Colored gravel can be used, as long as it is professionally made, certain cheaply made color gravels can be toxic to fish in your aquarium.
3. Make sure you ask plenty of questions when you are buying accessories or fish for your aquarium. The salespeople are there to help you, and should be able to handle any concerns you have when buying items for your aquarium.