How Many Fish Can Be In A 3-Gallon Tank? Best Fish & Stocking Ideas (2024)

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Just got your first fishbowl on a whim? Wondering how many fish can be in a 3-gallon tank? Read this nano-aquarium stocking guide first! A tank this small is easier to overcrowd than you can imagine.

Following the “1 inch of fish per gallon of water” rule of thumb, you can put three 1-inch fish in a 3-gallon tank. You can also keep invertebrate tank mates with one 2-inch fish, like a betta.

You can unknowingly overstock a 3-gallon tank even if you bring home just one pet fish. As juveniles, many large-bodied fish species can easily fit in a nano tank. A 6-month-old fancy goldfish can be just 2-inches long but will grow up to be 6-inches long as an adult.

Nano fish, which grow no more than 2-inches long as adults, are perfect for stocking a 3-gallon tank.

Factors That Influence How Many Fish You Can Keep In A 3-Gallon Tank

Going by the “1 inch of fish per gallon of water” rule, you can safely keep three 1-inch fish in a 3-gallon tank. This guideline does have its flaws, as it doesn’t take the behavior/temperament of fish into account.

You also have to consider the fact that your nano tank’s capacity drops as you start adding gear into it.

A filter, a heater, some décor, a live plant, even the substrate; all take up space in this already limited environment.

Fishkeepers often end up overstocking nano tanks. Even a small 6-individual school of nano fish can overwhelm a 3-gallon tank’s biofiltration system.

They simply produce more waste than the culture of good bacteria can convert into non-toxic nitrates. Water quality quickly drops dangerously low in an overstocked tank.

Solitary fish, or a group of invertebrates with a smaller bioload, are easier to keep healthy and content in a 3-gallon tank.

Best Fish To Keep In A 3-Gallon Tank

The best fish you can keep in a 3-gallon tank will typically display one, or all, of these 3 behavioral traits:

• Solitary – as they don’t feel the need to be surrounded by their peers. With a temperament that’s the direct opposite of that of shoaling/schooling fish, solitary species prefer living alone.
• Territorial – because they like claiming their habitat as their own, keeping territorial nano-fish as a single-species in a 3-gallon tank is preferred.
• Low bioload – critters that don’t create too much waste can be kept in larger numbers, like cherry shrimp and nerite snails. They will animate your nano tank and can also act as a cleaning crew.

Here’s a list of the 11 best fish and invertebrates to keep in a 3-gallon tank:

Betta Fish

A 3-gallon tank is the smallest home you can get for a betta, although they much prefer a minimum of 5 gallons!

Male bettas are territorial fish that can easily keep themselves entertained in a planted nano tank.

Endler’s Livebearers

Endler’s livebearers are best kept in groups with a 1:2 male to female ratio. The population can grow quickly because they’re prolific breeders.

They animate a nano tank even in small groups of 3 and are easy to care for.

Neon Tetras

Tetras are generally considered schooling fish, but they can feel safe traveling in groups of 3.

Neon tetras are eye-candy, contrasting the lush-green background of a planted 3-gallon tank!

Pea Puffers

Pea puffers are small enough to fit 2-3 of them in a 3-gallon tank, but their temperament makes that a bad idea.

Keeping just one dwarf pufferfish is ideal, as they’re not social critters. These tiny & feisty carnivores prefer a solitary existence.

Harlequin Rasboras

Harlequin rasboras have a mesmerizing metallic coloration that you’ll have a hard time looking away from!

They should be kept in groups of at least 2 individuals, but they can easily share a 3-gallon tank with some invertebrates.

Least Killifish

Also known as dwarf livebearers, least killifish are among the lowest-maintenance nano fish.

They do best in heavily planted set-ups, and you can expect them to be peaceful inhabitants when kept in pairs.

White Cloud Mountain Minnows

You can safely keep a pair of white cloud minnows in a 3-gallon tank. You can even skip the heater when setting up your nano aquarium.

They are cold-water fish and among the hardiest nano fish in the fishkeeping hobby.

Celestial Pearl Danios

Celestial pearl danios are also known as galaxy rasboras, with an appearance that resembles a burst of color.

They’ll peacefully go about their business when kept in groups of 3, making great tank mates for a few cherry shrimps.

Honey Gouramis

Keeping a pair of honey gouramis in a 3-gallon tank puts you near the stocking limit of your nano tank.

They make great beginner fish for a novice fishkeeper. Avoid keeping 2 males together.

Cherry Shrimp

You’ll be surprised how impressive an invertebrate-only planted tank can look. Some fishkeepers even prefer shrimp to stocking 3-gallon tanks with fish.

You can keep up to 10 cherry shrimp in a nano tank, as their bioload is minimal.

We have an entire article on how many cherry shrimp per gallon you can keep. Click here to check it out!

Nerite Snails

Nerite snails are popular among fishkeepers, as they’re ravenous algae eaters. You can keep them with most of the fish on this list, except bettas.

Avoid overfeeding the tank mates of a pair of nerite snails. The population can explode easily.

Check out our post on how many nerite snails you can keep per gallon!

Popular Fish Combos To Stock A 3-Gallon Tank

Tank mate compatibility is one of the most important factors to consider when stocking any fish tank.

If you’re looking to stock a 3-gallon tank with more than one species, compatibility becomes crucial.

In larger aquariums, fish have room to hide from each other, to define distinct territories, and to just simply avoid one another in general. In nano tanks, avoidance is rarely an option.

Here are some popular fish & invertebrate combos to stock a 3-gallon tank:

Combo #1

• 1 Betta;
• 5 Cherry Shrimp.

Combo #2

• 10 cherry Shrimp;
• 2 Nerite Snails.

Combo #3

• 2 Honey Gouramis;
• 5 Cherry Shrimp.

Combo #4

• 3 Least Killifish;
• 1 Nerite Snail.

Check out some creative 3-gallon aquascaping and stocking options here:

Fish You Shouldn’t Keep In A 3-Gallon Tank

Aside from the obvious (fish larger than 2 inches), there are a few stocking scenarios you should avoid, even with smaller fish. A fish’s temperament and instinctual social behavior can influence whether a fish will thrive, or just survive, in a 3-gallon tank.

Solitary fish can appreciate having an entire tank to themselves. But active schooling fish can have a drastically reduced life expectancy when kept alone. They find safety in numbers, and the stress of being alone can put them at risk for diseases or worse.

Here’s a list of small fish that you shouldn’t keep in a 3-gallon tank:

• Active schooling fish

Extremely active nano fish that engage in schooling behavior (barbs, platies, pygmy cory catfish) shouldn’t be kept in a 3-gallon tank. Not only do they need to be kept in large groups (6-8 at least), but they also need a large open swimming area.

These fish are small enough to fit the “1 inch of fish per gallon of water” guideline, but keeping just one or two of them would be cruel. They become overwhelmed with stress when kept alone or even in small numbers.

Shoaling nano fish can be kept in groups of 3-4, especially if they’re livebearers. In this case, a 1:3 male to female ratio is best.

• Aggressive nano fish with other fish species

Dwarf pufferfish (pea puffers) are the best example of fish that you can’t keep with other fish, solely because of their temperament. They’re notorious fin nippers and can severely injure slower swimmers (like bettas).

Although size-wise they could be kept with other tank mates in a 3-gallon tank, they’re better off kept in pairs of 1 male + 1 female. Two male pea puffers kept together is another “great” recipe for disaster!

Even in larger tanks, these tiny menaces should only be kept with similarly-sized fish that are able to swim away quickly to dodge their attacks.

• Incompatible tank mates

Just like in larger community tanks, fish compatibility plays a huge role in how peaceful the atmosphere is inside your 3-gallon tank. While the aggressive behavior of pea puffers can become stressful, they won’t eat their tank mates.

This isn’t the case when keeping a carnivore with its prey as a tank mate. Betta fish will often feast on smaller snails, and they can even attack shrimp.

Tank mate incompatibility will depend on a fish’s individual temperament. Not all male bettas will attack their invertebrate tank mates. But, since they have less room to stay out of each other’s way, you should avoid keeping them together.

• Juveniles of large-bodied fish species

Goldfish are often sold as “fishbowl pets” because of the popular Hollywood movie trope.

As juveniles, goldfish can reach a size of 2 to 3 inches in their first year of life but can grow to be up to 6-14 inches when fully mature.

There is a myth that these larger-bodied fish will only grow as large as their tank is. The truth behind their stunted growth is that they won’t live long enough to outgrow their tanks.

They often don’t have enough room to swim. Water quality is often poor when keeping fish with a large bioload in a small aquarium. These circumstances combined can cause death-inducing stress levels in fish.

Best Live Plants For A 3-Gallon Tank

Even in a small enclosed habitat, like a 3-gallon tank is, a live plant can work wonders. It can help reduce the stress levels of your pet fish, giving them a safe place to rest. Fish can also use plants to get away from their tank mates for a while to avoid getting overwhelmed.

Planting live aquarium plants in a nano-tank is a great way to oxygenate the water without adding extra gear. Putting an air stone/air pump inside a 3-gallon tank, as well as running a filter, can create too much water turbulence.

As you can imagine, even choosing the ideal live plants has its limitations when it comes to 3-gallon tanks. To set up a nano planted aquarium, you’ll need to first make sure the tank has a full-spectrum light fixture to keep the plants healthy and vibrant.

High lights will keep plants growing shorter than low lights. Shorter plants that grow relatively small are better for nano tanks because they leave enough room for swimming.

Some plants typically grow attached to driftwood (Anubias, Java Fern, African Water Fern), or in rock crevices. You can use a suction cup to attach these plants to one of the tank’s walls. There’s not much room for driftwood in a 3-gallon tank.

Here’s a list of the best live plants for a 3-gallon tank:

• Java Moss;
• Java Fern;
• Micro Sword;
• Chain Sword Narrow Leaf;
• Anacharis;
• Cryptocoryne walkeri;
• Creeping Charlie (Micromeria brownei);
• Marimo Moss Ball.

How To Set Up A 3-Gallon Fish Tank

Fishbowls and nano-tanks are often mistakenly considered easier to set up and maintain than larger tanks. That’s why they’re often gifted to children, along with the first pet that they’re responsible for.

The truth is that smaller tanks are most times harder to manage than larger community tanks. Of course, a 3-gallon tank won’t be harder to maintain than a 300-gallon tank.

But, compared to a 20 or 50-gallon tank, keeping water conditions balanced in a 3-gallon tank comes with plenty of challenges.

Keeping the tank’s bio-filtration system, oxygenation, pH levels, and water temperature steady is a harder task to accomplish in a 3-gallon tank. Luckily, with the right gear, this task is 100% achievable!

Here are the basics that you’ll need to set up an easy-to-maintain 3-gallon tank:

• Filter with an adjustable flow rate

Filtration is a must in nano-tanks, as they’re more prone to biological imbalances. A compact corner filter is ideal space-wise since it won’t get in the way too much.

Make sure you get an appropriately-sized filter for the volume of water inside a 3-gallon tank. A filter that’s too strong or just too big for your setup can be dangerous for your fish.

• Bacteria starter

Cycling a 3-gallon tank is just as crucial, if not more, than cycling larger tanks. Use a bacteria starter to put your aquarium’s biofiltration system in motion.

This will jumpstart the culture of beneficial bacteria in your nano tank and prevent the water from going toxic when first introducing fish.

• Heater, if you’re keeping tropical fish

Bettas, and other tropical aquarium fish, need a constant temperature ranging between 75-80°F. This is almost impossible to achieve without a submersible tank heater.

For a 3-gallon tank, you’ll need a 10–15-watt heater.

• Substrate, Sand, or Gravel

A layer of nutrient-rich substrate is highly recommended if you’re planning a planted 3-gallon tank setup. Rooted live aquarium plants need substrate to anchor their roots.

Substrate, gravel, or sand, are also beneficial for the tank’s biofiltration system. Beneficial bacteria have room to grow and spread there. Nitrifying bacteria will help improve the water quality inside your 3-gallon tank.

• Aquarium test kits

The biggest challenge in setting up a 3-gallon nano tank is maintaining stable water chemistry. Because there’s such a small volume of water, the waste that your fish produce will accumulate at a fast rate. That’s why water quality can fluctuate harsher in a nano tank than in a larger aquarium.

Use freshwater aquarium test kits to take the guesswork out of the equation. You’ll be able to monitor pH, ammonia, nitrite, and nitrate levels. These water quality indicators will let you know if you need to do water changes more often or if your tank cleaning routine is efficient.

What To Avoid When Setting Up A 3-Gallon Tank

There are several things you should avoid when setting up your 3-gallon tank:

• Plastic plants

Avoid including them in your setup, especially if you’re keeping a betta fish in your 3-gallon tank. Their long-flowing fins can easily tear or get snagged by fake plants.

If you’re not willing to give live aquarium plants a chance, choose artificial silk plants instead.

• Decorations with sharp edges

With limited space for swimming, decorations with sharp edges can cause plenty of injuries. Bettas, in particular, are clumsy swimmers that will bump into décor items when startled.

Choose round river stones and smooth decorations with crevices that fish can easily use as hiding spaces. These, along with living plants, will keep stress levels low among your nano fish.

How Often Should You Clean A 3-Gallon Fish Tank?

Generally speaking, you’ll need to get on a once-a-week cleaning schedule to keep your 3-gallon tank safe for its inhabitants.

Keeping water quality at a reasonable level and the water parameters stable will be your two main goals. That’s why the frequency of your cleaning sessions can vary, depending on:

• how efficient your filter is;
• how heavily stocked your 3-gallon tank is (no more than 85% of its capacity);
• whether it has been cycled or not;
• how often and how much you feed your fish (avoid overfeeding!).

Here’s a basic maintenance routine you can follow to keep a 3-gallon tank clean:

Make sure you perform these maintenance tasks on an alternating schedule. You shouldn’t siphon the gravel at the same time as you clean/change the filter media. And never deep-clean a 3-gallon tank!

The presence of beneficial bacteria is vital to the well-being of your fish. That’s why you need to clean your nano tank without losing the established culture of nitrifying bacteria.

Check out the basics of an efficient fish tank cleaning routine here!

Conclusion

A 3-gallon tank is the smallest recommended setup for fish, and it does come with a list of challenges.

Stocking your nano tank with the right fish species is step one in a successful and safe setup.

Staying on top of a regular maintenance routine should also be considered a top priority.

If you’ve purchased a 3-gallon tank and you’re disappointed by the limited stocking options, don’t give it up just yet. Even if you upgrade to a larger tank setup, this nano aquarium will make a great quarantine tank for new fish, or sick fish. You can also use it as a breeding tank or as a nursery for fry later on.

Recommended Reading:

• How Many Platies In A 10 Gallon Tank Can You Keep?