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Though many goldfish are doomed to life inside a glass sphere, fishbowls are generally not spacious enough for a goldfish to be happy and healthy. A 20 gallon (75.7L) is ideal for your first goldfish, as it can hold 2-3 fancy goldfish if you decide to increases your fish forces. The type of goldfish you have will help determine the size of tank they'll need. Fancy goldfish can be kept in a 10 gallon (37.9L) tank, but bigger goldfish like comets need a tank of around 50 gallons (189.3L). For each additional goldfish you add to your aquatic family, increase the capacity of your fish tank by roughly 10 gallon (37.9L) for each additional fish. Gravel is necessary to help maintain the water quality of your tank and to keep your goldfish happy. Goldfish are scavengers. They will pick up pieces of gravel and toss them back and forth, or just gum them for a while with their fish lips. Accordingly, choose gravel that is made up of individual pieces that are too large for the fish to swallow. Further, goldfish are curious, and benefit from incredibly short memories. Provide your goldfish up with ample rocks, caves, or artificial plants. A well-decorated tank can provide them with a lifetime of adventure. Your selection of decor, including natural or artificial rocks and plants must follow the following guidelines: Don't use wood. Though that piece of driftwood from your beach walk does look spectacular, it will likely discolor your fish tank's water and may even turn to mush. Beware of materials that may affect the pH of the water. If you're adding stuff you find outside, even just rocks and sea-shells, check your pH frequently. Don't place anything sharp in your fish tank. If your goldfish becomes frightened and move quickly, they may injure themselves. Goldfish are notoriously aggressive with plants. While gravel can defend itself, plants will easily get torn up by the voracious behavior of your goldfish friends. Some plants are more resilient, and tend to get along better with goldfish generally. Gravel and natural plants in particular provide more than an inviting ambiance they also help keep the biological environment inside the tank stable, so include at least a few natural plants in your tank. Try Vallisneria types, different Hygrophilas, Red Bacopa or even Ludwigia Arcuata.

Summary:
Choose an appropriate container to house your goldfish. Cover the bottom of the tank with appropriately sized gravel. Decorate your goldfish's domain. Only put certain natural plants in your goldfish tank.