Goldfish Tanks: How to Set up, Sizes, & Tank Mates

Goldfish tanks are tanks designed specifically for keeping goldfish. Some of the most important things to consider when selecting a tank for goldfish are the size of the tank, what material the aquarium is made of, and where the tank will be kept.

The best goldfish tanks are between 20 and 40 gallons and are made of glass or acrylic. Most goldfish tanks for beginners are kits that include the essentials: a good water filter and a dechlorinator, the right kind of substrate, decorative live plants, functional lighting, and some water testing kits.

Goldfish Tank Sizes

A goldfish tank should be at least 20 gallons because adult goldfish are considered large aquarium fish that grow up to 6 to 7 inches long. A single fish requires a 20-gallon tank, and each additional goldfish requires 10 gallons more — for example, a 30-gallon tank for 2 goldfish or a 40-gallon tank for 3 goldfish.

There are various types of goldfish, including single-tail goldfish, like common goldfish, or double-tail goldfish, such as fancy goldfish. Some fancy goldfish varieties grow up to 8 inches long and require at least a 20-gallon, 3-foot-long tank. Common goldfish, or comet goldfish, grow up to 10 inches and require a 30-gallon, 4-foot-long tank to thrive.

Goldfish Tank Size for One Goldfish

The minimum tank size for one goldfish is 20 gallons. A long 20-gallon tank is typically 2.5-feet long and 1-foot high, while a tall 20-gallon tank is 2 feet long and 1.3 feet high.

The minimum tank size varies for fancy goldfish, common goldfish, and comet goldfish. Fancy goldfish are the smaller of the three and require a tank of only 20 gallons. Common goldfish and comet goldfish are larger, each requiring a 30-gallon tank measuring 3 feet long by 1.5 feet high.

Goldfish Tank Size for Two or More Goldfish

The minimum tank size for multiple fish is 30 gallons, but larger tanks should be used for more than two fish. A 30-gallon fish tank works well for two 8-inch fancy goldfish. For each new fancy goldfish, the tank size should be increased by at least 10 gallons. For example, a group of three fancy goldfish requires a 40-gallon tank.

The perfect tank size for two or more common goldfish is 40 gallons, plus another 12 gallons for every extra fish — 52 gallons for three common goldfish, for example.

Equipment Needed to Set up a Goldfish Tank

To keep the goldfish safe and healthy, the aquarium should be equipped with good lighting, functional water filters, a net, a dechlorinator, an air pump, decorations, plants, and sand or another appropriate substrate. All of the items necessary for a goldfish tank can be purchased separately from aquarium stores, and most of the equipment is included as part of a starter kit.

Goldfish tanks don’t need heaters because these fish prefer cool temperatures. This species is endothermic, which means the fish depend on their external environment to regulate their internal body temperatures. If the temperature in your home drops significantly at night, a heater should be added to the fish’s tank. Though goldfish can survive in cold water, they prefer temperatures between 68 and 74°F.

Lighting

Proper lighting in the aquarium helps the fish process vitamins and minerals, encourages plants in the tank to grow quickly, and promotes harmony among plant and fish species.

Use fluorescent lighting to illuminate tanks that also receive plenty of natural light during the day. Use LED lighting in tanks that don’t receive much daylight. LEDs are small, cheap, energy-efficient, and illuminate medium-sized tanks well.

Filters

A good water filter installed in the goldfish tank maintains good water quality, which reduces the spread of diseases. Select an appropriate filter based on the design you prefer, the size of the tank, and your budget. Even the cheapest filter does a good job of filtering the majority of waste.

Substrate

A good substrate helps mimic the fish’s natural environment and helps fish adapt to tank life. Medium-sized gravel is dangerous for goldfish because the fish tend to dig the substrate in search of food and may swallow and choke on the pebbles. Choose aquarium sand or large rocks to prevent health issues in your goldfish and to ensure the tank looks good.

Plants & Decorations

Some goldfish are energetic and others are slow swimmers, but all goldfish are active fish and need enough room to swim around. Keep the number of decorations in a goldfish’s tank to a minimum. Use smooth rocks and artificial or live plants that won’t damage the fish’s delicate fins.

Goldfish dig in the substrate and may uproot plants. Secure plants by pressing them down with larger rocks. The best live plants for a goldfish tank thrive in high pH levels and include java ferns, anubias, Amazon swords, and crypts.

How to Set up a Goldfish Tank: Step-by-Step Instructions

These simple step-by-step instructions for beginner aquarists are helpful for setting up a goldfish tank and ensuring the goldfish is introduced into its new home safely.

Buy an Aquarium

Select the aquarium that’s the right size for the number of fish that’ll be kept in the fish tank. If more fish will be added to the tank later, buy a bigger tank ahead of time to save money and effort. For one goldfish, choose a tank of at least 20 gallons, or at least a 30-gallon tank for two or more goldfish. The best home for goldfish is a thick glass tank or an acrylic tank.

Choose the Right Place for the Tank

Choose a flat surface with enough space for the tank, and make sure the tank can’t be reached by children or pets. Place the tank away from direct sunlight because too much light can harm the fish. Avoid areas near cooling or heating systems, which affect the temperature of the water in the tank and stress the fish.

Add Substrate to the Tank

Cover the tank bottom completely with sand or rock substrate. A good formula to follow is 1 pound of substrate per 1 gallon of water.

Decorate the Goldfish Tank

Add decorations to the fish tank, including the rocks and plants. Carefully put the plants in the substrate and press them down with larger rocks to stop the goldfish from digging them up.

Install a Water Filter

Install a water filter in the tank. Water filters can be either external (placed on the outside of the tank) or internal (located inside the tank). External filters are more powerful and work better for a larger tank, while a smaller tank is best equipped with an internal filter.

Attach the filtration system to the tank following the instructions on the box.

Fill the Tank With Water and Let It Rest

Fill the planted goldfish tank with tap water, add a water conditioner to stabilize chlorine levels, use a pH kit to test the water’s pH (pH should be between 7.2 and 7.5), and let the tank sit for a few weeks before adding the fish.

Letting the tank rest before adding fish encourages beneficial bacteria to create a naturally safe environment similar to the goldfish’s natural habitat.

Add the Goldfish to the Tank

Once the pet goldfish is selected and brought home, it’s time to add it to the aquarium. First, place the bag with the fish in the fish tank and let it float for 15 to 20 minutes to let the fish adjust to the water temperature. Then, add some of the tank water into the bag. After 10 more minutes, gently take the goldfish out of the bag and put it into the aquarium, ensuring that none of the water from the bag is poured into the goldfish tank.

Best Goldfish Tank Mates

Goldfish are friendly freshwater fish that can share large tanks with other goldfish and other species. Great tank mates for your goldfish include:

• Rubbernose or bristlenose pleco
• Catfish
• Platy fish
• Other goldfish
• White cloud mountain minnows
• Dojo loach
• Cherry shrimp
• Mystery snail

The best tank mate for a goldfish is a fish that is used to cooler temperatures and doesn’t show aggression by getting territorial. Plecos and platy fish make excellent tank mates for a goldfish because they’re calm and adaptable. Non-fish species that make good tank mates for a goldfish and make the tank more fun to watch include small shrimp and snails.

How to Choose a Goldfish Tank

Some of the key factors to consider when choosing a perfect aquarium for your goldfish and tank mates include the tank’s construction materials, price, and space availability at home.

Construction Materials & Quality

Some of the most popular materials for fish tanks are glass and acrylic. Goldfish tanks made of thick glass are heavier but much more affordable and can even be purchased second-hand from other fish owners. An acrylic fish tank is lightweight and is considered more efficient to have at home because it’s much easier to move. However, an acrylic tank is significantly more expensive than a glass tank.

Price

A goldfish tank can cost from $50 to over $1,000. Prices vary depending on the tank material, brand, size, and equipment that comes with the tank. A good way to save money on an aquarium is to find available options from local fish clubs.

Location

Before buying a fish tank, consider the amount of available space at home where the goldfish aquarium will be located. The best place for a tank is far from any cooling or heating systems, and near (but not in front of) a window. Too much light during the day provokes excessive algae growth that lowers the water quality in the aquarium.

Conclusion: Is a Goldfish Tank Right for you?

The best goldfish tank is a large-size tank that holds between 20 and 40 gallons. Goldfish tanks can be made of either glass or acrylic and have a variety of additional equipment installed to keep the tank clean and maintain a good environment for goldfish.

Goldfish tanks suit aquarists who are prepared to free up enough space in their home to keep the goldfish in a large aquarium. A goldfish tank provides any aquarist with a beautiful space to keep and display their goldfish.

Goldfish Tank FAQs

Here are the answers to common questions about caring for goldfish and buying the right goldfish tank:

How Many Goldfish Can Be in a 10-Gallon Tank?

A 10-gallon tank can fit one small goldfish. However, a 10-gallon tank is a rather small tank for the goldfish species because these fish tend to grow up to 8 to 10 inches in length and require more space to thrive. If the space in your home is scarce, a 10-gallon tank can be suitable for a single adult goldfish, but not more. To keep multiple fish in one tank, choose a 20- or 30-gallon tank to provide goldfish with enough space.

How Long Do Goldfish Live in a Tank?

With proper care, goldfish can live in a fish tank for over 10 years. Some fancy goldfish varieties can live up to 30 years if a good fish-keeping practice is maintained. However, goldfish don’t often survive in a fish tank for such a long time due to inappropriate housing conditions and low water quality.

How to Clean a Goldfish Tank?

To clean a goldfish tank, change the water in the aquarium once a week and add conditioned water, remove the algae from the walls of the tank, and remove the floating debris from the top of the tank. Goldfish are messy fish that tend to dig in the substrate for food and may dig up aquarium plants. The fish produce a lot of waste, which is why goldfish tanks can get dirty quickly.

Why Is My Goldfish at the Bottom of the Tank?

Goldfish tend to swim at the bottom of the fish tank when they’re sick. If you notice the goldfish spending time at the bottom of the tank, it might have health issues like parasites, stress due to improper water conditions, or swim bladder problems. Most goldfish health issues can be resolved by changing the water in the tank or changing the fish’s diet.

What Do Goldfish Like in Their Tank?

Goldfish like a spacious tank with a variety of plants and smooth rocks. These fish love a varied diet that includes live brine shrimp, fish flakes, daphnia, and vegetable mix. The quality of water is important for goldfish: water should have a pH level of 7.5 and a cool temperature in the range of 68 to 74°F.