10 Terrific, Tiny Freshwater Fish for your Nano Aquarium

In recent years, the aquarium industry has seen a surge in demand for nano tanks. With their small size and compact filtration systems and lighting, they can easily become the focal point of any room in the house.

However, setting up a nano aquarium requires a fair amount of planning. After all, the compact size also means you must be efficient with how you use the space. However, it doesn’t mean you have to skimp on quality or creativity.

In this article, we will provide an overview of nano aquariums and share our top 10 favorite fish for our nano aquarium ecosystems.

Nano Aquariums

There is no real consensus on the definition of a nano aquarium tank. Most aquarists tend to agree that any tank less than 20-gallons is a nano tank; however, some retailers market tanks as large as 30-gallons as nano tanks.

Tank size has been further delineated with the addition of the pico tank. Pico tanks are considered to be any aquarium tank that is five gallons for less. While many fish species work for both nano and pico aquariums, the pico aquarium can be especially successful for some of the smallest freshwater fish on the market.

For more information, see The Best Fish for a 5 Gallon Tank.

It’s easy to mistakenly believe that the smaller the tank, the easier the upkeep will be. After all, there are a number of benefits to the nano system, such as:

  1. The startup and maintenance costs are lower.
  2. The tank and associated equipment do not take up as much space.
  3. Routine maintenance events typically take less time.

While there are certainly benefits to smaller tanks, they nonetheless provide their own unique challenges. Some of the main obstacles to nano tank ownership include:

  1. The smaller water volume means that the tank is more susceptible to changing water temperatures and conditions.
  2. The tank needs more frequent water changes to maintain water chemistry.
  3. There is less room for tank design.
  4. There is less room for fish, so it is much more important to pick fish that coexist well.

However, if you understand the requirements of nano tanks, they can be fantastic canvases in which to create unique, breathtaking marine ecosystems.

The Nitrogen Cycle and Nano Tanks

By far, the biggest challenge with nano tanks is managing the nitrogen cycle. When fish urinate and defecate in their tank, it releases ammonia into the water. Ammonia is highly toxic to fish and, if left unattended, will kill off your fragile ecosystem.

The ammonia produced by fish can be consumed by bacteria, which in turn produce either nitrite or nitrate. While nitrite is also toxic to fish, nitrate is a far less toxic alternative. Nitrates can be removed from the water by live plants or through water changes.

The nitrogen cycle is, therefore, the circulation of nitrogen (as ammonia, nitrite, and nitrate) through the tank.

aquarium nitrogen cycle diagram

Because nano tanks have a smaller volume of water, the ammonia, nitrite, and nitrate build-up in the tank is much quicker. However, it is not unmanageable. To prevent the nitrogen cycle from negatively impacting the health of your tank’s inhabitants, make sure you remember to do the following:

  • Perform fishless tank cycling. Fishless cycling is the process of establishing the good bacteria in your tank before introducing your fish. By creating good bacteria colonies in your tank prior to adding fish, you significantly reduce the chances of your fish dying from ammonia toxicity.
  • Perform weekly water changes. The quickest way to remove ammonia, nitrites, and nitrates from your tank is to remove the water. Remember- the smaller the tank, the more frequent your water changes will be. Most nano aquariums require weekly or bi-weekly water changes.
  • Invest in good filtration. The bacteria that break down ammonia will primarily reside in your filtration system. Therefore, the better your filtration system, the less you’ll have to worry about changes in your water chemistry. For nano tanks, we recommend investing in a filtration system that has a “gallons per hour” (GPH) rating that is at least four times your tank volume. For example, if you have a 10-gallon tank, make sure your filtration system is at least a 40 GPH system.

Once you have set up your tank décor and performed your fishless tank cycling, you are now ready to begin adding your small freshwater fish.

Top 10 Tiny Freshwater Fish for Nano Aquariums

1. Ember Tetra

Ember Tetra

    • Experience Level: Beginner
    • Temperament: Peaceful
    • Maximum Size: 0.8”
    • Minimum Tank Size: 10 gallons
    • Lifespan: 2-3 years
    • Diet: Omnivore

At only 0.8” when full-grown, Ember Tetras are considered to be the smallest member of the tetra family. Their size, combined with their brilliant orange-red, translucent bodies, make them the perfect addition to any nano aquarium.

Though Ember Tetras’ space requirements are small, they are exuberantly active swimmers that prefer longer aquariums to maximize their swimming space. They are a tight schooling fish, so the larger your school, the better the fish will look at the happier they will be.

When creating a habitat for your Ember Tetra, keep in mind that their colors will be most resplendent in a well-planted tank. They prefer tanks with lots of live plants, driftwood, and logs to mirror their natural habitat. However, make sure you also leave them plenty of room to swim.

Like most tetras, Ember Tetras are friendly, considerate tankmates that will coexist nicely in nearly any peaceful tank. As one of the only schooling fish small enough to thrive in a nano ecosystem, they can be the perfect centerpiece for your tank.

2. Pygmy Corydoras

Pygmy Corydoras

    • Experience Level: Easy
    • Temperament: Peaceful
    • Maximum Size: 1.3”
    • Minimum Tank Size: 10 gallons
    • Lifespan:3 years
    • Diet: Carnivorous

If you’ve chosen to add Ember Tetras to your nano tank, then Pygmy Corydoras are also must-haves. The Pygmy Corydoras (or Pygmy Cory) is a peaceful fish that gets along wonderfully with Ember Tetras, as well as other active fish.

Pygmy Corydoras are identified by the single, bold black streak that runs the length of their silver bodies. Though they are not the flashiest fish on this list, their muted colors serve as the perfect palette complement to their brighter tankmates.

Make sure you have a sandy substrate so that your Pygmy Corydoras don’t hurt their mouths and whiskers. They will also be happiest in a tank that has plenty of hiding places, such as caves and plants.

The coolest thing about Pygmy Corydoras is that, although they are a member of the Corydoradinae sub-family, they don’t exhibit many of the characteristics typically associated with other corydoras.

Most noticeably, they split their time between foraging in the lower water column and shoaling with other Pygmy Corydoras in the middle water column. If you’ve ever wanted a bottom-dweller that was just as likely to be perched up in the plants, this is the fish for you.

3. Endler’s Livebearer

Endler Livebearers

    • Experience Level: Beginner
    • Temperament: Peaceful
    • Maximum Size: 1.0-1.8”
    • Minimum Tank Size: 5-10 gallons
    • Lifespan: 2-3 years
    • Diet: Omnivorous

Male Endler’s Livebearers look like vibrant paintings fresh from the mind of Jackson Pollock. With their whimsical colors and schooling behaviors, these fish are a favorite among nano tank enthusiasts.

Endler’s Livebearers are one of the easiest species to keep if you are new to the hobby. They are accepting of a wide variety of water conditions and are easy-going when it comes to food preferences.

Though they are friendly fish when interacting with their tankmates, male Endler’s Livebearers can be territorial with other Endler’s Livebearer males. To avoid aggression, keep them in a heavily-planted tank to minimize line-of-sight encountered.

Endler’s Livebearers have personalities as vibrantly unique as their coloration. While this makes them friendly tankmates, it can also make them a bit of a challenge for aquarists. They are incredibly inquisitive fish that are known to leap out of their tanks. They have even been known to channel their inner Nemo and get stuck in rocks, plants, and filters. Therefore, it’s important to make sure you Endler’s Livebearer-proof your tank prior to introducing them.

4. Scarlet Badis

Scarlet Badis

    • Experience Level: Intermediate
    • Temperament: Semi-Aggressive
    • Maximum Size: 0.8”
    • Minimum Tank Size: 10 gallons
    • Lifespan: 3 years
    • Diet: Omnivorous, but primarily carnivorous

When you see the Scarlet Badis, it’s hard to understand why it is not in every single aquarium around the world. After all, its vibrant red and blue coloration, its fascinating sexual dimorphism (males are larger with prominent ventral fins), and its enthusiastic personality check nearly every aquarium enthusiast’s box.

However, while these marvelous fish are a fantastic addition to nano aquariums, they come with more challenges than many of the fish on this list.

Scarlet Badis are friendly fish that peacefully exist in most peaceful and semi-aggressive aquarium ecosystems. However, they are known to be aggressive towards one another, and therefore are best when housed singly. If you do add more than one to your tank, ensure that there is plenty of live plants and decorations to block the line of sight and give each fish space from other members of the species.

Scarlet Badis are also incredibly picky eaters. Though they are technically omnivores, most prefer meaty foods. The vast majority of Scarlet Badis will refuse flakes, and therefore require live feedings of brine shrimp, small snails, and worms.

However, if you are willing to put up with the eating habits and extra bio loads of these fish, they are sure to be a spectacular addition to your nano tank.

5. Sparkling Gourami

sparkling gourami

    • Experience Level: Beginner
    • Temperament: Peaceful
    • Maximum Size: 1.0-1.5”
    • Minimum Tank Size: 10 gallons
    • Lifespan: 4-5 years
    • Diet: Omnivorous

The Sparkling Gourami, also known as the Pygmy Gourami, is the smallest member of the Gourami family. Sparkling Gouramis are clearly identified by the iridescent red, blue, or green dots that dominate their bodies and fins.

Sparkling Gouramis are naturally found in ditches and ponds (and sometimes even rice fields) in Southeast Asia, and are therefore accustomed to fluctuating environmental conditions. In fact, Sparkling Gouramis have a labyrinth organ that helps them survive in poorly-oxygenated water.

Sparkling Gouramis prefer tanks that have plenty of live plants, floating plants, and driftwood. They will be more adventurous and active in the tank with plenty of hiding spaces and when added in groups of three or more.

Whenever possible, try to house in groups with only one male to avoid male mating disputes. However, sexting these fish is challenging and requires someone to shine a light on their body and check for the presence of female sexual organs. If your pet store is unable to sex the fish, it is best to house Sparkling Gourami singly.

6. Least Killifish

Least Killifish

    • Experience Level: Beginner
    • Temperament: Peaceful
    • Maximum Size: 1.5”
    • Minimum Tank Size: 3 gallons
    • Lifespan: 3 years
    • Diet: Omnivorous

Despite the name, Least Killifish are not actually members of the Killifish family. Also known as Mosquito fish, this small species more closely resembles a guppy or molly. In fact, these little fish are the smallest livebearer fish discovered to date!

If you are looking for an easy, low maintenance fish, we cannot recommend the Least Killifish enough. They are extremely resilient, will thrive in a wide range of water temperatures and conditions, and will eat pretty much anything you feed them.

Least Killifish are peaceful, friendly fish who will do well with most other small, peaceful fish. It is essential that you don’t put them with aggressive or large fish because, given their size and temperament, they are easily bullied or eaten by tankmates.

Though their color isn’t the more vibrant, their sleek bodies and sharply-contrasting colors give them a subdued beauty that is downright mesmerizing. Whether you add one individual or several, these wonderful fish are some of the best nano tank fish.

7. Norman’s Lampeye Killifish

Norman Lampeye Killifish

    • Experience Level: Beginner
    • Temperament: Peaceful
    • Maximum Size: 1.5”
    • Minimum Tank Size: 10 gallons
    • Lifespan: 3 years
    • Diet: Carnivorous

Contrary to their ominous name, Norman’s Lampeye Killifish are not aggressive; in fact, they can peacefully coexist with most peaceful nano tank species. However, the name isn’t all inaccurate.

Norman’s Lampeye Killifish are known for the horizontal crescent at the top of their eye that appears to glow (like a lamp) under the aquarium light. Their glowing eyes, combined with their shiny blue scales, make them a gorgeous addition to any tank.

Like most bright fish, Norman’s Lampeye Killifish will thrive in darker tanks with plenty of live plants. As an added perk, the more dark hiding spaces you give them, the more their glowing eyes will pop.

Norman’s Lampeye Killifish are shoaling fish that spend most of their time at the top of the water column. They do best in groups of 3 to 5, as the added numbers give them more confidence when moving around the tank. However, because they are an active species in the upper water column that is prone to jumping, make sure you have a secure lid on your aquarium.

8. Sixray Corydoras

Sixray Corydoras

    • Experience Level: Beginner
    • Temperament: Peaceful
    • Maximum Size: 1.0”
    • Minimum Tank Size: 10 gallons
    • Lifespan: 5 years
    • Diet: Omnivorous

Sixray Corydoras, or False Corydoras, are close relatives of the Corydoras family. They can be distinguished based on their dorsal fin rays (Sixray Corydoras have 6 rays while members of the Corydoras family have 7 rays) and distinct coloration.

Sixray Corydoras are adorable, small fish with black and white striations and distinct black and white translucent fins. Their bubbly personalities are perfectly exemplified in their adorable mustache-like barbels.

Found in the tropics of Brazil, these fish do best in tanks that mirror their natural environments. Sixray Corydoras prefer tanks with lots of live plants and soft, sandy substrates to protect their barbels.

Sixray Corydoras are mellow, easy-going omnivores that happily spend their time foraging at the bottom of their tank. They are gregarious fish that, in addition to multiple tankmates, enjoy being kept in groups of 4-6.

If you are a beginner aquarist or just someone looking to create a low-maintenance tank, these resilient, friendly fish are the perfect addition to your nano aquarium.

9. Celestial Pearl Danios

Celestial Pearl Danios

    • Experience Level: Beginner
    • Temperament: Peaceful
    • Maximum Size: 1.0”
    • Minimum Tank Size: 5-10 gallons
    • Lifespan: 3-5 years
    • Diet: Omnivorous

Celestial Pearl Danios, also known as CPDs, are beautiful blue fish with silver and gold spots that mimic the shining stars of the night sky. Their celestial bodies are beautifully accentuated by their vivacious red and orange fins, which flow gracefully as they swim.

CPDs are schooling fish that are happiest in groups of 4-6. While they can survive in a 5-gallon tank, a school of this size will be much more content in a tank that is closer to 10-gallons.

Though CPDs are incredibly friendly to other fish, male CPDs will fight aggressively with each other over mating rights. Therefore, it is best to either limit your tank to one male and multiple females, or to ensure that your female population outnumbers your males.

Because these fish were discovered in 2006, they are relatively new to the aquarium world. This means that aquarists are still discovering the optimal conditions that they prefer. Therefore, if you are an adventurous person who enjoys the challenge of exploring the unknown, this could very well be the perfect fish for you.

10. Chili Rasbora

Chili Rasbora

    • Experience Level: Beginner
    • Temperament: Peaceful
    • Maximum Size: 0.75”
    • Minimum Tank Size: 5 gallons
    • Lifespan: 4-8 years
    • Diet: Carnivorous

Chili Rasboras, also known as Mosquito Rasboras, have one of the most memorable color palettes of any fish in the aquarium world. With their fantastically-vibrant reds contrasting their deep navy blues and blacks, the Chili Rasbora almost looks like a cartoon fish that has been enthusiastically colored.

However, these fish are very much real. Chili Rasboras are incredibly social, outgoing fish that will thrive in most peaceful nano aquariums. If you want a tank that is active and exciting, these fish are the perfect addition. Their curious, outgoing natures ensure that they will spend the day busily dashing from one area of the tank to the next.

Chili Rasboras prefer to be kept in large groups of 6 or more individuals. In fact, the more fish you add to their school, the more confident and outgoing they will be.

Chili Rasboras do best in ecosystems that mimic the natural conditions of tropical waters. They like tanks that are heavily planted with plenty of decorations and floating plants.

Though they don’t require it to be content, Chili Rasboras do best in blackwater biotopes. The tannins released in blackwater tanks both highlight their dazzling coloration and boost the Chili Rasboras’ immune systems.

Final Thoughts

Though nano tank fish are small in stature, their looks and personalities are larger than life. This list is but a small fraction of the number of incredible fish that the aquarium trade has to offer.

When choosing fish for your nano aquarium, make sure you take the time to ensure that you are not only creating a beautiful ecosystem, but also a healthy one. By focusing on choosing fish that can happily eat, play, and live together, you will be ensuring that your wonderful, imaginative ecosystem will quickly spring to life.

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