15 Flagship Small Freshwater Fish for Nano Tanks

There  are some stunning nano fish available in the aquarium trade.

It’s easy to see why nano tanks have become a craze. They’re beautiful, compact, and fit lots of different budgets and living situations.

In this guide, I’ll share with you my top 15 fish for nano tanks and how to set one up.

Nano tanks are smaller setups, usually 20 gallons or under, that are tailored towards creating a tiny ecosystem. They come in all kinds of configurations, but most people also include live plants in their nano tanks.

Nano tanks have become wildly popular over the last few years. They’re favored because they’re a smaller investment than larger setups and can fit in almost any house or apartment.

Nano tanks might be small in size, but they still offer a wide variety of options for decoration and configuration. You can create a miniature garden, a tiny mountain range or a submerged jungle, the possibilities are endless.

And there are many small but vibrant species of fish and invertebrates that you can add to a nano tank that are just stunning.

15 Fish for Nano Tanks

Pro Tip: All tank sizes listed in this article are absolute minimums. The greater the water volume, the easier it is to maintain healthy water conditions.

I really don’t recommend a tank smaller than 5 gallons, especially for a beginner. Going at least a little bigger is always better.

1. Chili Rasbora (Boraras brigittae)

Schooling/shoaling fish: yes. Keep in a group of six or more.

Description: Chili Rasbora, sometimes called mosquito rasboras, are tiny shoaling fish native to Borneo. Their bodies are an unbelievably bright red with an iridescent black stripe down the side that gets thinner as it nears the tail.

They’re active and cute, one of those fish that are always doing something when you look in the tank.

Size: 0.75 inches (1.9 centimeters)
Minimum tank size: 5 gallons
Care level: easy
Temperament: peaceful
Temperature: 68°-78°F (20°-25.5°C)
pH: 5.0-7.0
Diet: carnivore – crushed flake, baby brine shrimp or live or frozen daphnia.

2. Neon Tetra (Paracheirodon innesi)

Neon tetras swimming in school in aquarium

Schooling/shoaling fish: yes. A group of six or more is best.

Description: Neon tetras are some of the most popular fish in the aquarium trade. They have a bright blue head that tapers to a bright red tail. They’re a long, thin-bodied fish with small fins.

They are native to the Amazon River basin where they shoal together in huge groups that can number in the thousands.

They can be kept in a 10 gallon, but the bigger the tank, the more interesting their behavior.

Size: 1.2 inches (3 centimeters)
Minimum tank size: 10 gallons
Care level: easy
Temperament: peaceful
Temperature: 72°-76°F (22.2°-24.4°C)
pH: 6.0-7.0
Diet: omnivore – high quality flake food, micro pellets or baby brine shrimp

3. Cardinal Tetras (Paracheirodon axelrodi)

The cardinal tetra (Paracheirodon axelrodi) is a freshwater fish

Schooling/shoaling fish: yes. They do best in a group of six or more.

Description: Cardinal tetras look very similar to neon tetras, but with some subtle differences.

They get almost an inch bigger than neons. Cardinals have the same long, thin body shape, and also have blue and red stripes, but these extend the entire length of their bodies, instead having a blue head and a red tail.

They are another peaceful shoaling fish that likes to be kept in large groups. They love to dart in and out of tall plants.

Size: 2 inches (5 centimeters)
Minimum tank size: 15 gallons
Care level: easy
Temperament: peaceful
Temperature: 72°-76°F (22.2°-24.4°C)
pH: 6.0-7.0
Diet: omnivore – high quality flake food, small pellets, brine shrimp and live or frozen daphnia.

4. Bettas (Betta splendens)

Betta fish in a planted aquarium

Schooling/shoaling fish: no. Males should be kept by themselves. You can have a group of three or more females, but watch out for aggression.

Description: Bettas have a pointed snout and long laterally compressed body. But what really sets them apart are their beautiful elongated fins and bright colors, especially the male of the species.

Many male bettas do not play well with others so you should count on keeping them alone.

Size: 2.25 inches (5.7 centimeters)
Minimum tank size: 5 gallons
Care level: easy
Temperament: aggressive, males should be kept alone
Temperature: 75°-81°F (23.8°-27.2°C)
pH: 6.5-7.5
Diet: carnivore – Bettas eat mostly insects in the wild so it’s best to feed them things like Fluval Bug Bites Betta Formula, frozen or freeze dried bloodworms or live daphnia.

5. Harlequin Rasboras (Trigonostigma heteromorpha)

Schooling/shoaling fish: yes. They do best in a group of six or more.

Description: Harlequin rasboras have a deep chest that narrows to a much thinner tail. Their heads, backs and tails are a really pretty orangish red and their bellies are silver.

On each side of their bodies they have a black marking shaped like a funnel that runs from their dorsal fins to their tails. I really think they’re stunning.

Size: 2 inches (5 centimeters)
Minimum tank size: 10 gallons
Care level: easy
Temperament: peaceful
Temperature: 72°-81°F (22.2°-27.2°C)
pH: 6.0-7.5
Diet: omnivore – high quality flake foods, live or frozen daphnia and bloodworms.

6. Fancy Guppies (Poecilia reticulata)

Many guppy fish in aquarium

Schooling/shoaling fish: yes. Best kept in a group of either all males or one male and 3 or 4 females.

Description: Fancy guppies come in a huge variety of colors. They have a long, slim body shape. Females are a subdued silver color but males have enlarged, colorful tails.

In some color variants, color extends along the entire length of the body. These little guys can have lots and lots of babies, so consider keeping just males.

Size: 2 inches (5 centimeters)
Minimum tank size: 5 gallons
Care level: easy
Temperament: mostly peaceful. Males can sometimes harass females and each other.
Temperature: 70°-82°F (21.1°-27.7°C)
pH: 7.0-8.0
Diet: omnivore – micro pellets, high quality flake food, frozen brine or mysis shrimp.

7. Endler’s Livebearers (Poecilia wingei)

Male black-bar Endler

Schooling/shoaling fish: yes. Best kept in a group of either all males or one male and 3 or 4 females.

Description: Endlers are probably my favorite livebearer. They are closely related to guppies and have the same body shape but males are so brightly colored they look like you gave a small child neon markers and asked them to draw a fish. There are several different color variations available.

Just like guppies, Endlers breed like crazy. Consider keeping a group of all males.

Size: 1-1.8 inches (2.5-4.5 centimeters)
Minimum tank size: 5 gallons
Care level: easy
Temperament: peaceful
Temperature: 75°-80°F (°-°C)
pH: 7.0-8.0
Diet: omnivore – micro pellets, flake food, frozen bloodworms and mysis shrimp are good choices.

8. Zebra Danios (Danio Rerio)

Best freshwater fish for beginners Zebra Danios with distinctive horizontal zebra stripes swimming against soft green plants background. Soft focus

Schooling/shoaling fish: yes. Should be kept in a group of five or more.

Description: Zebra danios have a long slim body shape with small rounded fins. Their bodies are silver with bright metallic blue stripes that run from nose to tail. They are extremely active and should be put in as large a tank as possible.

Size: 2.5 inches (6.3 centimeters)
Minimum tank size: 15 gallons
Care level: easy
Temperament: peaceful
Temperature: 65°-77°F (18.3°-25°C)
pH: 6.5-7.5
Diet: omnivore – high quality flake food, micro pellets, live or frozen daphnia or bloodworms.

9. Bluefin Notho (Nothobranchius rachovii)

Bluefin notho swimming in planted tank

Schooling/shoaling fish: no. They are best kept with one male to several females.

Description: Bluefin nothos are a kind of killifish. In the wild, they live in tiny bodies of water that dry up every year. The adults die off, leaving only their eggs.

Because of this, notho killifish only live for 1-2 years. They are a slim, long-bodied fish with bright red coloration. The body is covered with metallic blue spots. The fins and tail have bright blue stripes, very striking.

Size: 2.4 inches (6 centimeters)
Minimum tank size: 5 gallons
Care level: moderate
Temperament: semi-aggressive, especially between males
Temperature: 68°-75°F (20°-24°C)
pH: 6.0-7.0
Diet: predator – frozen and live foods like daphnia, baby brine shrimp, bloodworms and cyclops

10. White Cloud Mountain Minnow (Tanichthys albonubes)

Schooling/shoaling fish: yes. Should be kept in groups of six or more.

Description: White cloud mountain minnows are a long-bodied, slim fish. Their bodies can range from a bright golden color to a silvery blue and their fins and tails are bright red.

These minnows are commonly bred as a feeder fish for larger species, but they really are beautiful when properly cared for. They are a cold water species that does not need a heater.

Size: 2 inches (5 centimeters)
Minimum tank size: 10 gallons
Care level: easy
Temperament: peaceful
Temperature: 45°-70°F (7.2°-21.1°C)
pH: 6.0-8.0
Diet: omnivore – flakes, micro pellets, live and frozen daphnia, baby brine shrimp and bloodworms.

12. Celestial Pearl Danio (Danio margaritatus)

Schooling/shoaling fish: yes and no. They will sometimes group together, but other times they will not. It’s best to keep one male to three or four females.

Description: the celestial pearl danio (aka galaxy rasbora) is a slim, long-bodied fish with small pointed fins. Its body is dark blue and covered with golden spots.

This gold color also runs along their backs. Females have bright orange bases on their fins and tails. Males have large patches of red and black on their fins. They are gorgeous.

Size: 1 inch (2.5 centimeters)
Minimum tank size: 10 gallons
Care level: moderate
Temperament: males will fight over mating rights. Provide lots of hiding places.
Temperature: 73°-79°F (22.7°-26°C)
pH: 6.5-7.5
Diet: omnivore – flake food, micro pellets, live and frozen foods.

13. Sparkling Gourami (Trichopsis Pumila)

Schooling/shoaling fish: no. But it can be kept in groups.

Description: the sparkling gourami has a laterally compressed body with a deep chest that tapers slightly towards the tail.

Their bodies are grey or beige with bright metallic red and/or blue speckles. Their fins and tail are almost transparent with rows of more metallic speckles. Their eyes are large and metallic looking as well.

Size: 1.5 inches (3.8 centimeters)
Minimum tank size: 10 gallons
Care level: moderate
Temperament: peaceful
Temperature: 76°-82°F (24.4°-27.7°C)
pH: 6.0-7.0
Diet: omnivore. This species does best if given a mix of animal protein and algae-based foods: high quality community flake food, spirulina, micro pellets.

14. Pygmy Corydoras (Corydoras pygmaeus)

Schooling/shoaling fish: yes. Corys absolutely need to be kept in a group of five or more to be happy. Larger numbers make them feel more secure.

Description: Pygmy corys are adorable miniature catfish. They are active bottom dwellers that have a slightly humped back. Their foreheads are steeply sloped up to the hump at their dorsal fin.

From there, the body tapers down towards the the tail. These are great little cleaner fish and frankly, their behavior in a big school is pretty funny. They act like a pack of hyper little kids let loose in a candy store.

Size: 1.2 inches (3 centimeters)
Minimum tank size: 10 gallons
Care level: easy
Temperament: peaceful
Temperature: 72°-79°F (22°-26°C)
pH: 6.4-7.4
Diet: omnivore – sinking foods like pellets and wafers. They also love frozen bloodworms and gel foods like Repashy Bottom Scratcher.

15. Oto Cats (Otocinclus macrospilus)

Otocinclus catfish in planted fish tank

Schooling/shoaling fish: yes. These do best in a group of five or more.

Description: Oto cats are dwarf catfish that feed on algae. They are a great addition to a community tank clean up crew. Frankly, I think they’re really cute and their behavior and interactions make them interesting. They remind me of naughty little kids.

Size: 2 inches (5 centimeters)
Minimum tank size: 10 gallons
Care level: easy
Temperament: peaceful
Temperature: 72-82°F (22-28°C)
pH: 6.0-7.5
Diet: herbivore – high quality algae wafer or blanched veggies like broccoli and zucchini.

How to Set Up a Nano Aquarium

Once you’ve decided on a species, you can figure out what the best setup for them will be.

The Nitrogen Cycle and Nano Tanks

One of the biggest considerations when setting up and stocking a nano tank is the nitrogen cycle. Once you’ve got fish in the tank…well…there’s not delicate way to say this, they poop and pee in the water.

I mean, it’s not exactly like they can go use a toilet.

That poop and pee sinks to the bottom of the tank where it starts to break down. This produces ammonia (NH3). Ammonia is really toxic for fish, or pretty much any living thing really.

As more waste is produced, more and more ammonia can start to build up in the water, making it completely unlivable.

Luckily, there are species of beneficial bacteria that can colonize our filters and substrate and help process fish waste.

There are several different kinds of bacteria that help process waste in an aquarium. One kind eats ammonia and puts off a chemical called nitrite (NO2 -1). It’s pretty toxic too, but luckily there is another kind of bacteria that quickly eats the nitrite and turns it into nitrate (NO3-).

This conversion of ammonia to nitrite and then nitrate is what is referred to as the nitrogen cycle.

But this bacteria doesn’t show up instantly, it takes time to get the bacteria up and running in your tank.

Pro Tip: It’s best to get the nitrogen cycle going in your tank before you ever add fish. Fishless cycling is more humane and can save you from losing fish to ammonia and nitrite poisoning. Steps to perform a fishless cycle can be found here.

Nitrates are much less toxic than ammonia or nitrite. However, over time, they can build up to toxic levels in the water column. High levels of nitrate can stress and even kill fish.

And, since nitrate is acidic, it can start to drop the pH of your water. This can also stress and kill fish.

This is why it’s so important to do water changes each week. When you take water out of the aquarium, you take the nitrate with it.

Pro Tip: The smaller your tank is, the more quickly nitrates build up. This means that you will have to do more water changes more often. A bigger tank is more forgiving since there is a larger volume of water

Tank Size

This is probably the most important factor you have to decide on. Tank size determines what kind of fish you can keep, how many fish you can stock, what kinds of plants you can include, how often you need to do maintenance, etc.

I really would not recommend going with a tank smaller than 5 gallons.

Going with a super small tank means that you have to do more water changes, even for a single fish like a betta.

Bigger is always better for fish tanks.

The larger water volume means there is more volume to dilute waste.

Think about it this way. Imagine a dog in a fenced yard. If the yard is only 12 feet by 12 feet, it is quickly going to be overrun with dog poop. And you’ll need to clean it every few days.

Take the same dog and put them in a yard that’s 40 feet by 40 feet and there’s a lot more room for poop. And you can go longer in between cleaning up the waste.

It’s the same principle with aquariums. It’s just water instead of grass.

More water means that it takes longer for fish waste to negatively impact water quality. So you can go longer between water changes.

I would really recommend going with a 20 gallon tank if at all possible. The cost difference between a 10 gallon and a 20 gallon is not that much. And a 20 gallon isn’t a huge whopper of a tank that takes up a bunch of space either.

With something like a 20 gallon, you may only need to do a water change once a week. Whereas, with a 5 gallon, you’d likely need to do 2-3 water changes each week.

Filtration

Choosing the right filtration for your nano tank is critical.

You should be able to find a rating for your filter, a measurement of gallon per hour (GPH). The GPH lets you know how many gallons of water the pump in the filter can move each hour.

As a general rule, you want your filter to have a GPH that is at least four times the capacity of your tank.

For example, on a 10 gallon tank, you’d want a filter that has a GPH of at least 40.

Another consideration, research your species and find out if they like a strong current. Some species of fish, like bettas, aren’t the strongest swimmers. They do much better with a filter that produces a gentle flow.

One of the things that I look for when I’m buying a filter is biomedia capacity. Biomedia is filter media, like ceramic rings, lava rock, bio balls, sponges, etc. Biomedia is what the beneficial bacteria in your filter grow on.

The more biomedia your filter can hold, the more room there is for beneficial bacteria to live.

Plants and Decor

How you plant and decorate your tank should really be determined by the species of fish you want to keep.

Some species want a densely planted tank. Others may want open swimming areas. You may need to add some some small caves or hiding places.

It all depends on what’s best for the fish.

One thing that I can recommend for pretty much all nano tanks is live plants.

They improve your water quality by taking up nitrates and phosphates and they’re beautiful. Basically, they’re awesome.

Substrate

There are a lot of choice when it comes to the substrate that you use for your nano tank.

Gravel

Doesn’t change water chemistry
Variety of colors and textures
Not great for rooted plants

Sand

Looks really natural
Can get sucked into filters and damage motors/impellers
Doesn’t provide nutrients for rooted plants

Soil

Great for rooted plants
Can be pretty pricey
Has to be replaced every few years

Pro Tip: Some plant substrates can change your water chemistry, leaching minerals and lowering pH. Be sure to research substrates before you add one to your tank.

Lighting

Here’s the thing about lighting, it’s more for us than the fish. Fish do need a reliable day/night cycle, but they don’t need super bright overhead lights to get it.

Lights on the tank are mostly for live plants and so we can see the fish. Base your lighting on what your live plants need and your own personal tastes.

Pro Tip: Some fish prefer dim lighting. You may need to change your lighting choices and plant selections to make these fish more comfortable.

Heating

Whether or not you need to heat your tank depends on the species you keep. Most nano fish come from tropical regions and absolutely need a heater.

But some species prefer cooler temperatures.

The decision to add a heater, or not, is all about what’s best for the fish.

Final Words on Fish For Nano Tanks

There really are some stunning nano fish available in the aquarium trade. Highlighting these gorgeous little fish shows that great things come in small packages.

When deciding on what kind of setup to go with, it’s important to factor in the needs of the fish you want to keep. Your best bet is to tailor your tank around the species.

Remember that bigger tanks are actually easier to take care of in the long run. Plus, they give you more room for fish and plants.

It’s easy to see why nano tanks have become a craze. They’re beautiful but compact enough to fit lots of different budgets and living situations.

There are so many fun and creative things that can be done with these smaller tanks, the only limit is your imagination.

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In this guide, I'll share with you my flagship choices for the best small freshwater fish for nano tanks so you can set up a stunning aquarum at home #modestfish #aqaurium #fish #freshwater
Read on this article, we’ll share some tips, how to cycle your tank with the nitrogen cycle process that can helps avoid your fish’s waste releases ammonia into the water. #modestfish #aquarium #cleaning

Katherine Morgan

Hey, there! I'm Katherine from Northwest Florida. I've kept aquariums for over two decades, enjoy experimenting with low-tech planted setups and an avid South American cichlid enthusiast.
Katherine Morgan

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