How Many Neon Tetras In A 40-Gallon Tank?

Disclosure: When you purchase something through my affiliate links, I earn a small commission. As an Amazon Associate, I earn from qualifying purchases.

If you own a 40-gallon tank – this is great news. It is a pretty large tank that can easily accommodate small fish like neon tetras.

But how many of these can you keep? And what if you want to mix some other types of fish? How many of those you should get? And what about breeding?

In this article, I will answer all these questions. It is the ultimate guide for an aquarist who is interested in neon tetras and owns a tank of 40 gallons.

Let’s dive right in.

How Many Neon Tetras Can You Keep In A 40-Gallon Tank?

A 40-gallon tank can accommodate around 20-25 neon tetras comfortably, ensuring sufficient space for each fish and promoting a thriving habitat.

This estimation follows the commonly recommended rule of one inch of fish per gallon of water, taking into account that adult neon tetras typically grow to approximately 1.5 inches in size.

Calculating The Number Of Neon Tetras Suitable For A 40-Gallon Tank

Luckily, calculating the right number of neon tetras for a tank of 40 gallons is pretty straightforward:

  • Begin with the size of the tank, which is 40 gallons.
  • Apply the general guideline for fish stocking, which advises one inch of fish per gallon of water. For a 40-gallon tank, this suggests a maximum of 40 inches of fish.
  • Consider the size of the specific fish species, such as neon tetras, which typically grow to around 1.5 inches in length as adults.
  • Divide the total inches of fish allowed by the size of one fish. In this case, 40 inches divided by 1.5 inches equals approximately 26-27 neon tetras.
  • To ensure ample swimming space and maintain a healthy environment, it is recommended to stock fewer fish. Therefore, a suitable range of neon tetras for a 40-gallon tank would be 20-25 individuals.

Why Is A 40-Gallon Tank Ideal For Neon Tetras?

Offering your neon tetras with 40 gallons is an excellent choice, and for several reasons:

  • Room to Swim: Neon tetras are active swimmers. A 40-gallon tank, which translates to roughly 151 liters, offers ample space for these tiny, vibrant fish to dart around and explore, promoting their natural behavior and overall wellbeing.
  • Social Dynamics: Neon tetras are schooling fish, preferring to exist in groups. A 40-gallon tank can comfortably accommodate a school of around 20-25 neon tetras, which constitutes a healthy social environment for them.
  • Stable Water Parameters: Larger tanks, like the 40-gallon one, are less prone to rapid fluctuations in temperature and chemical composition. This stability is crucial for neon tetras, who thrive in consistent water parameters.
  • Naturalistic Habitat: A bigger tank provides enough space to include aquatic plants and decorations. These additions not only enhance the aesthetics of the aquarium but also mimic the natural habitat of the neon tetras, offering hiding and resting places.
  • Fish Compatibility: In a 40-gallon tank, there’s room to house other species alongside neon tetras, assuming they’re compatible. This option provides a more diverse, attractive, and dynamic aquarium community.

Also Read: Neon Tetra Tank Size

Tips For Successfully Raising Neon Tetras In A 40-Gallon Tank

Keeping neon tetras in 40 gallons isn’t that difficult, but there are some things to keep in mind:

  • Aquarium Set-Up: Start with a clean, well-cycled 40-gallon tank, ensuring that it’s free from harmful chemicals or toxins that could stress or harm your neon tetras.
  • Water Parameters: Neon tetras thrive in soft, slightly acidic water with a pH between 6.0 and 7.0. The temperature should be at 70-81°F (21-27°C).
  • Lighting: As forest stream dwellers, neon tetras prefer dimmed lighting. Too much light can stress these fish, so consider using adjustable LED lights that can mimic dawn, day, and dusk.
  • Feeding: Feed your neon tetras a varied diet of high-quality flake food, brine shrimp, daphnia, and bloodworms. Remember, their stomach is about the size of their eye, so feed them small amounts twice a day.
  • Tank Decorations and Plants: Mimic their natural habitat by adding live plants and driftwood. Plants like java moss or Amazon sword can provide hiding spots, reducing stress and creating a more natural environment.
  • Regular Water Changes: To maintain water quality, perform regular water changes, typically 10-20% of the tank volume every week. This helps to eliminate waste and keeps the water parameters stable.

Also Read: How Many Neon Tetras In A 30-Gallon Tank?

Does The Gender Of Neon Tetras Affect Their Numbers?

No, the gender of neon tetras does not inherently affect their numbers in a tank.

A balanced mix of male and female neon tetras can coexist peacefully, and their gender does not dictate the recommended quantity for a tank, which is usually based on tank size and the fishes’ social behavior.

Will A 40-Gallon Tank Become Overcrowded Due To Breeding?

Neon tetras breeding in a home aquarium is relatively rare as they require specific conditions for successful breeding and egg survival.

However, if those conditions were met and they did breed, a 40-gallon tank could eventually become overcrowded.

It’s crucial to monitor your tank and have a plan in place, such as a separate tank or a willing local fish store, to accommodate any potential offspring.

Is Breeding Neon Tetras Possible In A 40-Gallon Setup?

Yes, it’s possible to breed neon tetras in a 40-gallon tank, and here are some crucial steps to ensure successful breeding:

  • Create Optimal Conditions: Set the water parameters to mimic their natural breeding environment – a temperature around 77°F (25°C), pH level between 6.0 and 6.5, and a water hardness of 1 to 2 dGH.
  • Provide Adequate Food: Condition the prospective parent tetras with a high-quality diet rich in live or frozen foods like brine shrimp or daphnia to stimulate spawning.
  • Dim the Lights: Neon tetras prefer to spawn in low light conditions, so consider using dimmed lights or a blue light to simulate dawn, which is their natural spawning time.
  • Use a Spawning Tank: If possible, set up a separate spawning tank with a mesh bottom to protect the eggs from being eaten, as neon tetras, unfortunately, don’t have parental instincts and might consume their own eggs.

Frequency Of Neon Tetra Breeding

Neon tetras, when in optimal conditions, can breed every 1 to 2 weeks.

However, it’s important to note that achieving these conditions in a home aquarium can be challenging, making frequent breeding less common.

Also Read: How Many Neon Tetras In A 55-Gallon Tank?

Can You Add Additional Neon Tetras To A 40-Gallon Tank?

Yes, you can add additional neon tetras to a 40-gallon tank, provided it’s not already at its maximum capacity. Here are some tips on how to do this properly:

  • Assess Your Tank’s Capacity: Make sure your tank is not already full according to the stocking rule (one inch of fish per gallon). Overcrowding can lead to stress and disease.
  • Quarantine New Fish: Always quarantine new fish for two weeks before introducing them to your existing tank. This prevents the spread of potential diseases.
  • Acclimate the Fish: When introducing new neon tetras, acclimate them to the tank conditions by gradually mixing tank water into the bag they came in over a period of an hour or so.
  • Monitor Closely: Keep a close eye on the newly introduced tetras and existing fish for any signs of stress or aggression.
  • Feed Properly: Ensure all fish are getting enough food. Competition for food can create stress, particularly among new tank mates.
  • Regular Water Changes: To maintain water quality, perform regular water changes, typically 10-20% of the tank volume every week.

What Is The Minimum Number Of Neon Tetras?

A minimum of 6 neon tetras is generally recommended to ensure they exhibit their natural schooling behaviors and reduce stress.

However, ideally, keeping them in larger groups of 10-15 or more allows them to thrive, given adequate tank size and conditions.

Keeping Neon Tetras With Other Fish In A 40-Gallon Tank

Keeping only neon tetras in your fish tank can be pretty boring. Obviously, you’ll want to mix some other fish in your 40-gallon tank.

Here is a simple table I created that says how many of each fish you can keep:

Fish SpeciesRecommended Number in 40-Gallon Tank
Neon Tetras (only)20-25
Neon Tetras & GuppiesNeon Tetras: 20-25, Guppies: 15-20
Neon Tetras & MolliesNeon Tetras: 20-25, Mollies: 10-12
Neon Tetras & Zebra DaniosNeon Tetras: 20-25, Zebra Danios: 15-20
Neon Tetras & Platy FishNeon Tetras: 20-25, Platy Fish: 10-15
Neon Tetras & Betta FishNeon Tetras: 20-25, Betta Fish: 1

1. Neon Tetras And Guppies

You can keep around 20-25 neon tetras and around 15-20 guppies.

Guppies are peaceful and occupy the upper part of the tank, allowing neon tetras to swim freely in the middle.

2. Neon Tetras And Mollies

Around 20-25 neon tetras and approximately 10-12 mollies can be kept together. Mollies are larger and need more space, so fewer can be accommodated.

3. Neon Tetras And Zebra Danios

A combination of 20-25 neon tetras and around 15-20 zebra danios would work well. Zebra danios are active swimmers and can coexist peacefully with neon tetras.

4. Neon Tetras And Platy Fish

You can keep around 20-25 neon tetras and around 10-15 platy fish in a 40-gallon tank. Platies are slightly larger and also enjoy group living, so ensure they have enough room.

5. Neon Tetras And Betta Fish

In a 40-gallon tank, you can keep 20-25 neon tetras and 1 betta fish. Betta fish can be territorial, so only one should be kept in the tank to prevent aggression.


A 40-gallon tank can easily hold 20-25 neon tetras. As the minimum school size is six individuals, you are in a great spot.

You can also mix other types of fish pretty easily, including mollies, platy fish, zebra danios, and even aggressive fish like bettas.