How Many Goldfish In A 5 Gallon Tank?

Keeping goldfish as pets is a beloved pastime for many aquarium hobbyists. The sight of these vibrant fish gliding gracefully through the water can be utterly mesmerizing. However, there is an ongoing debate about whether a 5-gallon tank provides adequate space for goldfish.

Some argue that a 5-gallon tank is sufficient for a single fancy goldfish or a pair of smaller common goldfish. Others insist that nothing less than a 20-gallon tank is acceptable due to the large bioload goldfish produce. So how do you determine what is truly best for the health and wellbeing of your goldfish?

In this comprehensive guide, we will examine all angles of this issue. You’ll learn about the different types of goldfish, their specific needs, tank mate options, lifespan considerations, ethical factors, alternatives for smaller tanks, and proper goldfish care.

goldfish in a 5 gallon tank

Can 2 Goldfish Live in a 5-Gallon Tank?

While it is technically possible to keep 2 fancy goldfish or 2 slim-bodied common goldfish in a 5-gallon tank, it is far from ideal. Here are some key reasons why:

Water Quality Challenges

Goldfish have a high bioload, meaning they produce a lot of waste. This waste breaks down into ammonia and nitrites, which are highly toxic. In a small 5-gallon tank, levels can spike rapidly. Extra filtration and very frequent water changes would be required to control the buildup.

Even with diligent maintenance, water parameters tend to fluctuate more in tiny tanks. This stresses fish and leaves them vulnerable to disease. Goldfish thrive in stable, pristine water conditions.

Stunting and Deformities

When goldfish are confined to cramped quarters, their growth becomes stunted. The fish remain small but their internal organs continue growing, causing deformities and early death.

Providing adequate space allows goldfish to grow to their expected adult size and live a full lifespan. Common goldfish can reach 10-12 inches, while fancy varieties grow 6-8 inches on average.

Oxygen Limitations

Goldfish require highly oxygenated water. With only 5 gallons, dissolved oxygen levels can quickly drop to dangerous levels for two fish. Surface agitation and airstones help, but are only short-term solutions.

Behavioral Issues

Goldfish are active swimmers that need room to move about. In a 5-gallon tank, two fish would constantly be bumping into each other, causing stress. Lack of swimming space is mentally and physically detrimental.

Difficult Maintenance

As mentioned, goldfish have a heavy bioload. In a small tank, ammonia and nitrite levels rise quickly between water changes. At minimum, you would need to change 50% of the water 2-3 times per week. This amount of maintenance is quite unrealistic for most people long-term.

While you could technically add 2 small goldfish to a 5-gallon tank, you would be constantly battling water quality issues. The fish would likely suffer from chronic stress, behavioral problems, stunted growth and a shortened lifespan. For their health and wellbeing, a larger tank is highly recommended.

5-Gallon Tank Fish Combinations

If you already have a 5-gallon tank, you may be wondering what fish can live happily and healthily in that environment. Here are some great options for tank mates that won’t overload the limited space:


Guppies are a popular freshwater fish known for their bright colors and flowing fins. Males grow to about 1.5 inches, while females reach 2.5 inches. Their small size and low bioload make them ideal for nano tanks. You could keep 3-4 guppies in a planted 5-gallon tank. Just be sure to get all males or all females since they breed rapidly.

Endler’s Livebearers

Closely related to guppies, Endler’s livebearers max out around 1 inch in length. Groups of 4-6 would work well in a 5-gallon tank. Their active nature and vivid orange, blue and yellow patterns are sure to brighten up your small space.

Ember Tetras

At just 1 inch fully grown, ember tetras are perfectly suited for 5-gallon tanks. Their striking reddish-orange hue provides a pop of color. A school of 6-8 embers would look spectacular against a lush, planted backdrop.

Sparkling Gourami

Native to Southeast Asia, these tiny fish reach just over 1 inch long. They have an iridescent sparkle that gives them their name. A breeding pair or small group of 4 would happily reside in a 5-gallon environment.

Pygmy Corydoras

Bottom-dwelling pygmy cory cats grow under 1 inch in length. They are active scavengers that help keep the substrate clean. A group of 6 would complement a small school of tetras or guppies nicely.

Least Killifish

Least killifish are the smallest live-bearing fish species. Adults only reach about 0.75 inches long but produce bright colors. A trio can live comfortably in a 5-gallon tank.

Chilli Rasboras

At just 0.6 inches fully grown, chilli rasboras are tiny but make a big visual impact. Groups of 8-10 create movement and interest with their red coloration zipping around the tank.

Celestial Pearl Danio

Another nano fish, celestial pearl danios reach about 0.75 inches in length. Their tan bodies are dotted with white and orange spots for a unique look. Groups of 8-10 create mesmerizing schooling behavior.

Stick to fish under 2 inches long that prefer to live in small schools or pairs. This allows for adequate space and low bioload in a 5-gallon tank. Perform partial water changes each week and provide a gentle filter to maintain water quality.

How Long Can a Goldfish Live in a 5-Gallon Tank?

Sadly, goldfish will have a markedly shorter lifespan when confined to a small 5-gallon tank versus a properly sized aquarium. Here’s a look at average expectancy:

Common Goldfish

In optimal 75+ gallon aquariums, common goldfish can live 10-15 years. But in a cramped 5-gallon tank, their lifespan is reduced to just 1-3 years.

Fancy Goldfish

Oranda, ryukin, fantail and other fancy varieties enjoy lifespans of 10-20 years when housed in at least 30 gallons of water per fish. In a 5-gallon tank, the outlook is grim at just 1-4 years.

The drastic difference highlights why small tanks are detrimental. Goldfish growth becomes stunted, their organs fail, and they succumb to disease much sooner without adequate space.

Types of Goldfish Suitable for a 5-Gallon Tank

No goldfish are truly “suitable” for permanent housing in a tiny 5-gallon tank. However, some short-bodied varieties can potentially survive in these confines slightly better than others, if setup properly. Here are the “best” options:

Comet Goldfish

Comets are slim, streamlined single-tailed goldfish. They reach 10-12 inches in a proper environment but may stay under 4 inches when stunted in a 5-gallon tank. With very frequent water changes and only 1 fish, comets might survive a year or two.

Fancy Goldfish

The fancy varieties—like oranda, ryukin and fantail—have double tails that hamper movement. They have shorter bodies than common goldfish, maxing out around 8 inches long when healthy. In a 5-gallon tank, fancy goldfish might survive 1-3 years with meticulous care and just 1 fish.

Avoid Goldfish With Egg-Shaped Bodies

Egg-shaped fancy goldfish like ranchu, pom pom, pearlscale and lionhead suffer more severe effects from poor water quality. Their round bodies and swim issues make 5 gallons particularly problematic.

While no goldfish belong in a tiny 5-gallon tank, slim-bodied varieties with single tails fare best. Still, their health rapidly declines and lifespan is cut tragically short.

How Many Fish in a 5-Gallon Tank With a Betta?

The iconic betta fish can certainly live happily in a 5-gallon planted tank. However, their aggressive territorial instincts limit tank mate options. Here are some potential combinations:

  • 1 betta + a few snails/shrimp
  • 1 betta + 5-6 pygmy corydoras
  • 1 betta + 6-8 ember tetras/green neon tetras/chilli rasboras
  • 1 betta + 5-6 male guppies

Avoid bright, flashy species that resemble bettas. Overcrowding stresses bettas.

Gallons Needed for Multiple Goldfish

When keeping multiple goldfish, larger aquariums are a must. Here are the recommended minimums:

  • 2 fancy goldfish: 20 gallons
  • 2 common/comet goldfish: 55 gallons
  • 3 fancy goldfish: 30 gallons
  • 3 common/comet goldfish: 75 gallons
  • 4 fancy goldfish: 40 gallons
  • 4 common/comet goldfish: 90 gallons

As a general rule, fancy varieties need at least 10 gallons per fish. Common and comet types require 20-30 gallons each. Oxygenation is also critical with multiple goldfish, so powerful filtration and air stones are beneficial.

With adequate space, goldfish thrive and display their natural behaviors. Their bright colors and personalities really shine when kept humanely.

Goldfish Care and Maintenance

Caring properly for goldfish requires more than just an appropriate sized tank. Here are some key elements for a healthy environment:


Goldfish are messy fish with heavy bioloads. A strong filter rated for at least twice the tank volume helps maintain water quality. Canister filters work well for goldfish tanks.


Dissolved oxygen levels plummet quickly in goldfish tanks. Using air stones, powerheads and surface agitation prevents this. Check oxygen levels regularly.

Water Changes

To dilute nitrates and replenish minerals, change at least 25% of the water weekly. With extra fish or undersized tanks, changes up to 50% twice a week may be needed.

Water Parameters

Test for ammonia, nitrites, nitrates, pH and temperature routinely. Ideal ranges are:

  • Ammonia & Nitrites: 0 ppm
  • Nitrates: <20 ppm
  • pH: 6.5-7.5
  • Temperature: 65-72°F


Offer a varied diet of high-quality pellets, vegetables, live/frozen foods. Avoid excessive feeding to reduce waste.

Keeping Goldfish in a 5-Gallon Tank: Is It Ethical?

From an ethical standpoint, keeping goldfish in cramped 5-gallon tanks for their entire lives is highly questionable. Here’s why:

Lifespan Reduction

As previously covered, goldfish in tiny tanks only survive 1-4 years usually. Their lifespan is slashed by over 75% compared to properly kept goldfish. Knowingly stunting their lives seems morally wrong.


Between stunted growth, organ damage, oxygen deprivation and toxic water conditions, goldfish endure tremendous suffering in inadequately sized aquariums.

Natural Behavior Prevention

Goldfish are active swimmers built for speed and endurance. Taking away their ability to behave naturally by confining them goes against ethical keeping standards.

Difficulty Meeting Needs

No matter how hard you try, a 5-gallon tank simply cannot meet the complex needs of goldfish long-term regarding space, filtration, oxygenation and dilution of toxins. It sets them up for failure from the start.

For these reasons, putting goldfish in tiny tanks ultimately does more harm than good. Larger home aquariums or pond environments are truly what goldfish require to lead healthy, fulfilled lives.

Alternatives to Goldfish for 5-Gallon Tanks

If a 5-gallon tank is your limit, there are many vibrant, active small fish species that can thrive in a nano aquarium. Here are some top alternatives:

  • Ember tetras
  • Neon tetras
  • Guppies
  • Endler’s livebearers
  • Pygmy corydoras
  • Chili rasboras
  • Sparkling gouramis
  • Celestial pearl danios
  • Least killifish

With plants, rocks and driftwood, a 5-gallon tank can become a dynamic small-scale underwater world for more suitable species. Take time to research and select fish that are known for doing well in small tanks. This prevents inadvertently harming them.

Frequently Asked Questions

Do goldfish need a filter in a 5-gallon tank?

Yes, filtration is absolutely vital in any goldfish tank, especially smaller volumes. A 5-gallon tank cannot dilute waste buildup without strong mechanical and biological filtration. An external canister filter rated for at least twice the tank size is recommended. Avoid weak corner filters.

What temperature is best for goldfish in 5 gallons?

Ideally, 65-72°F is the target range. Warmer water holds less oxygen. Cooler temps help compensate for the oxygen limitation in a small tank. Use a submersible heater and thermometer to maintain a stable temperature within the ideal range.

Can I put rocks or gravel in a 5-gallon goldfish tank?

Bare-bottom is best, as waste collects in substrate and fouls the water rapidly. But if using gravel, choose a smooth type under 1/8” diameter. Avoid sharp rocks or substrates they can swallow. Ensure any decor won’t have sharp edges or leach chemicals.

How often should you feed goldfish in a 5-gallon tank?

Once daily is sufficient, and offer only what they can consume within 2-3 minutes maximum. Overfeeding fouls the water very quickly in a small volume. Vary their diet with flakes, pellets and treats like blanched veggies.

Do goldfish need air pumps in 5 gallons?

Definitely. Surface agitation via an air-powered sponge filter, air stone or bubble wand is critical for gas exchange. Oxygen saturation drops rapidly in limited water, so aeration is vital. Change the air stone monthly.

Can goldfish live alone in a 5-gallon tank?

While not ideal, a single fancy goldfish or slim-bodied common goldfish may survive short-term in 5 gallons with flawless maintenance. No tank mates should be added due to space constraints and territoriality of goldfish.

Is bottled bacteria beneficial in a 5-gallon goldfish tank?

Yes, bottled bacteria products can help jumpstart the nitrogen cycle more quickly and safely fish-in cycle a 5-gallon tank. Look for reputable brands that contain live nitrifying bacteria strains like Tetra SafeStart Plus. Shake well and dose per instructions.

How do I transport goldfish from a store to a 5-gallon tank?

Use an insulated cooler bag, battery-powered air pump with air stone, and double bagging method. This protects the fish during the stressful transport home. Float bag for 15 minutes to adjust temperatures before netting the fish into their new tank.


While it may seem harmless to add a goldfish or two to a spare 5-gallon tank, doing so creates an ethical dilemma. These fish quickly outgrow such confined spaces and suffer chronic stress, organ damage, oxygen deprivation and early death.

For the wellbeing of your goldfish, investing in a robust filtered tank of at least 20 gallons (or ideally a pond) is money well spent. Your fish will thank you by living their full 10-15 year lifespan in vibrant health!

If a larger tank is not possible, opt for naturally small species like tetras, rasboras or livebearers. They can genuinely thrive in a 5-gallon nano aquarium. Just be sure to research species specifics and properly setup the tank first.

With a little forethought and proper planning, you can have happy, healthy fish while avoiding inadvertently harming them through ignorance or negligence. The lives of your aquatic pets are in your hands!