Write an article based on this summary:

Rearrange the tank during your monthly cleaning. Add new items to the tank. Interact with your goldfish while feeding it. Never purposely scare your goldfish.
Move plants and items to different areas of the tank. This will create a whole new playground for your goldfish to play and explore. New items, such as new plants or items at the bottom of the tank, will give the fish new things to explore and interact with. Remember to only add items that are safe for the tank though, so go to your aquarium store and buy something new. Playing with your goldfish while you feed it is a good opportunity to train it and give it mental stimulation. In fact, goldfish can even be trained to ring a bell for food. This provides stimulation and fun for the goldfish. Interacting with your goldfish is especially important if it is the only fish in your tank. The interaction will give it stimulation that it's not getting from other fish. In order to keep your goldfish happy and healthy, you should strive to not scare or disturb it as much as possible. Doing things like tapping on the glass or putting your hand in the tank unnecessarily scares your goldfish, which puts stress on its health. Fish that are scared will go to hiding places in their tank. If you want to see your beautiful fish swimming around, don't scare them into hiding.