You should use gravel designed for the purpose, which you can get from a pet shop. The individual stones should be around 3mm in diameter. Before you put the gravel into the tank, make sure you rinse it properly in tap water. It is a good idea to add a few plants to your tank. Goldfish enjoy swimming among plants and nibbling them.
Plants also help to keep the water clean, and produce oxygen in the daytime.
Remember to wash them in tap water before adding them to your tank. Net You should buy a small fine net from your pet shop. This will allow you to catch any sick fish easily. There is a wide range of foods available. The best type is flakes or pellets, which have been designed specially for goldfish.