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How Many Tetras In A 3-Gallon Tank? Will Small Tank Stunt Growth?

How Many Tetras In A 3-Gallon Tank? Will Small Tank Stunt Growth?

Neon tetras are the poster child of fish suitable for small tanks. But how small is too small for these fish? How many neon tetras in a 3-gallon tank?

A 3-gallon tank is quite small – no wonder. And while it may look more manageable and easy to care for, small tanks don’t offer much room for mistakes. A momentary lapse and things can go south in an instant. 

In this blog, we will discuss the correct number of different kinds of tetras for a 3-gallon tank. 

How Many Tetras In A 3-Gallon Tank?

We can use the ‘one inch per gallon’ rule for small fish that don’t grow over 3 inches long. So, going by the formula, the ideal number of tetras in a 3-gallon tank is 2-4. You can add 2 neon tetras that grow around 1.5 inches long. As for small ones like ember tetras, you can add 4. 

The “one inch per gallon” rule is very much debatable. That’s because it doesn’t consider the fish’s height, the area needed for swimming, ammonia spikes, and the space taken by gravel and decors during calculation. 

Imagine adding a 20-inch catfish in a 20-gallon tank! 

However, this rule is safely applicable for fish smaller than 3 inches. And since neon tetras seldom grow bigger than that, we will be using this rule to calculate the ideal number of different tetra species for a 3-gallon tank.

Related: How Many Neon Tetras In A 10-Gallon Tank? 

How Many Neon Tetras In A 3-Gallon Tank?

neon tetra

On average, neon tetras grow around 1.5 inches (4 cm) long. So, when we divide 3 by 1.5, we get 2. 

So, you can house 2 neon tetras in a 3-gallon tank. However, neon tetras are schooling fish. They’d do best in a group of at least 6-10. 

How Many Ember Tetras In A 3-Gallon Tank? 

ember tetra

Ember tetras grow slightly smaller than their neon cousins – reaching about 0.8 inches (2 cm) long on average. So, when we divide 3 by 0.8, we get 3.75

Now you can either round it off to 3 or 4. So, the answer would be 3-4 ember tetras in a 3-gallon tank. 

How Many Glofish Tetras In A 3-Gallon Tank? 

glofish tetra

In general, glofish tetras grow around 2 inches (5 cm) long in captivity. So, when we divide 3 by 2, we get 1.5. 

Once again, you can round off 1.5 either way – 1 or 2. But we’d love to house at least 2, wouldn’t we? 

However, note that these ‘mutant’ fish are reported to grow albeit longer than 2 inches in some cases. Therefore, you might have to purchase a bigger tank for them down the road. 

How Many Cardinal Tetras In A 3-Gallon Tank?

cardinal tetra

In captivity, cardinal tetras can reach a length of 1.25 inches (3 cm) and weigh around 0.004 ounces. Females are usually longer and wider than males. 

When we divide 3 by 1.25, we get 2.4 

Therefore, we can house 2 cardinal tetras in a 3-gallon tank. But if you’re feeling adventurous, you might add 3. The trade-off here would be that you should be more vigilant of the tank’s parameters comparatively.

How Many Emperor Tetras In A 3-Gallon Tank?

emperor tetra
Credits: 7TP (Creative Commons license)

Usually, emperor tetras clock in at 1.6 inches (4.2 cm). 

Thus, when we divide 3 by 1.6, we get 1.8. 

And you know the drill. We can round off 1.8 to 2. 

So, you can house 2 emperor tetras in a 3-gallon tank. However, note that you may have to relocate them to a bigger tank as they grow. 

That’s because males tend to get quite aggressive towards each other when competing for a female’s attention. 

How Many Congo Tetras In A 3-Gallon Tank? 

congo tetra

Congo tetras grow bigger than all the other variants that we mentioned above. They can grow between 2.5 to 3 inches (6.3-8.5 cm). 

So, if we follow the ‘one rule per gallon’ rule, you can only house 1 congo tetra in a 3-gallon tank

And since it’s never a good idea to keep any fish alone, you might want to purchase a bigger tank and some friends for your congo tetra. 

How Many Buenos Aires Tetras In A 3-Gallon Tank?

buenos aires tetra
Credits: L Jerry3388 (Creative Commons license)

Buenos Aires tetras usually grow up to 3 inches (7.6 cm) on average. Therefore, technically, you can only house one of them in a 3-gallon tank

However, Buenos Aires are pretty active and aggressive compared to other tetra species. Therefore, the recommended tank size for these fish is 30 gallons. 

But as I read on forums, some hobbyists have raised them in a tank as small as 1- gallon as well. 

How Many Serpae Tetras In A 3-Gallon Tank?

serpae tetra
Credits: Faucon (Creative Commons license)

Serpae tetras grow around 2 inches (5 cm) long. 

So, when we divide 3 by 2, we get 1.5. 

Once again, you can either round it off to 1 or 2. However, note that serpae tetras are mildly aggressive fish. Therefore, they need plenty of space. 

If you want to raise, it’s best that you invest in a bigger tank – preferably 20 gallons and above. 

4 Disadvantages Of Keeping Tetras In A 3-Gallon Tank

It’s natural to think small tanks are easier to tend. But the opposite is true. A number of caveats come attached with a small tank. The water parameters are more volatile, and mistakes are often magnified. In turn, they make fish prone to stunted growth and stress. 

Stunted Growth 

Several pieces of research suggest that fish release certain pheromones in the water that hinder the growth of other fish. 

Most of these studies focus on fish from the carp family, like goldfish. However, we cannot rule it out entirely for tetras as well. 

In a closed and congested system like a 3-gallon tank, these pheromones have nowhere to go except inside a fish’s body – potentially interrupting the fish’s physical growth. 

And it’s not just the pheromones that inhibit a fish’s growth in a cramped tank. Lack of exercise, stress and polluted water are directly linked to poor health and stunted growth. 

High Stress Levels 

A cramped tank is a foolproof recipe for stress in fish. An overcrowded tank directly translates to a lack of enough swimming space and territory to claim. 

And as mindless as we assume fish to be, they’re highly sensitive beings with unique needs. 

So, a small tank with a lack of swimming space and hiding places only adds to your fish’s stress. 

Toxic Environment 

As a matter of fact, small tanks are actually a lot more challenging to keep and take care of than larger tanks. That’s because even the slightest fluctuations in the water parameters are magnified in a small tank and can potentially be catastrophic. 

As I always say, the smaller the tank, the bigger the room for mistakes. So, if you are a beginner, I definitely don’t recommend getting a 3-gallon tank. At least go for 10 or 20 gallons. 


Tetras are schooling fish. In the wild, they school in a group of thousands. And they just don’t do it for fun. They do it to protect themselves from predators better, forage well, and swim more efficiently. 

You are practically depriving your tetra of its natural instincts in a tank without much space or friends. With nowhere to go and nobody to be with, these active and inquisitive fish will definitely get bored in a small tank. 

How To Keep Tetras In A 3-Gallon Tank?

If you are not someone who takes no for answers, here are a couple of things you can do to keep tetras in a 3-gallon tank. They are: performing routine water changes, adding minimal decors, and installing reliable equipment. 

Let’s have a look at these pointers in brief. 

Perform Routine Water Changes 

As I have so many times already, smaller tanks are prone to more volatile and abrupt water changes. The buildup of harmful compounds like ammonia and nitrite happens quite fast. 

And mind you, tetras are super fragile when it comes to ammonia. 

The answer to the right frequency and extent of water change will differ from one hobbyist to another. I’d suggest going with 30-35% water change weekly, given the tank is fully cycled and rightly stocked. 

However, the rules for water change aren’t carved in stone. Feel free to modify it depending on your tank’s size and stocking numbers. 

Don’t Add Many Decors 

There’s simply not enough room in a 3-gallon tank to add decorations or play up with aesthetics. 

A few rocks for caves and a plant that rises to the tank’s mid-level would suffice. 

If you go overboard with the decors, this will quite profoundly hinder the tetras’ swimming ability. These active swimmers prefer open spaces.

Don’t Add Any Other Creature 

A 3-gallon tank does not offer enough room to add any other fish or crustaceans alongside tetras.

If you are feeling adventurous, you can try adding ghost shrimps, so they keep the tank clean. But we definitely cannot rule out the chances of them being eaten by tetras. 

Invest In Reliable Equipment 

Beginners often assume a tank as small as 3 gallons is self-sufficient and doesn’t need to be reinforced with equipment. Unfortunately, that’s the farthest from the truth. 

A 3-gallon tetra tank very much needs a filter, a heater, and an air pump. 

The filter should be gentle yet potent enough to eliminate the day-to-day gunk the tetras produce. 

The temperature should clock in somewhere between this range: 72-76 degrees Fahrenheit (22-24 degrees Celsius).

And lastly, an air pump that offers an output of 0.099 liters per minute to ensure proper oxygenation. 

However, if the tank is planted, the pump should have 0.079 liters per minute air output. 

How Many Tetras In A 3-Gallon Tank? Real Answers By Real People

I’ve put together a bunch of relevant comments left by hobbyists on forums for you to read. 

This is what their opinions look like on stocking tetras in a 3-gallon tank:

Note: All the opinions expressed below purely belong to the respective authors.

“Tetras would be a bit cramped in there. If you upgrade to a 10-gallon tank, you will have more options.”

“Adding tetras to a 3-gallon tank would be cruel. You might be able to add a snail or a shrimp in there, but nothing else.”

“Neon tetras in a 3-gallon tank is not a good idea as they are schooling fish. You’d need at least 5-6.”

A 3-gallon tank aquarium is very small. For any fish to do well, it needs enough space to swim and exhibit its true behavior. Fish need to be kept in groups to feel secure and go well. 

As long as you keep up with water changes, they should be fine in a 3-gallon tank. But for a beginner, I would recommend a 20-gallon tank. 

Frequently Asked Questions 

How Much Does A 3-Gallon Tank Weigh? 

A 3-gallon fish tank weighs 3lb when empty and 27lb when filled with water typically. 

How Big Is A 3-Gallon Tank? 

In general, most 3-gallon tanks have the following dimensions: 12″ x 6″ x 8″ (L x W x H)

If you’re interested to read up about weight and dimensions for tanks ranging from 2 and a half to 225 gallons, check out this article

How Many Neon Tetras In A 3-Gallon Round Tank?

A 3-gallon tank can house 2-3 neon tetras. However, we don’t recommend keeping fish in a 3-gallon tank. 

In round tanks, the surface to air ratio is compromised. Also, maintaining the temperature is difficult in small tanks. 

A 3-gallon round tank’s measurements usually go like this: 11.25″ x 11.25″ x 11″ (L x W x H). And it weighs around 0.8 lb. 

Final Words: How Many Tetras In A 3-Gallon Tank? 

You can stock around 2-4 tetras in a 3-gallon tank. 

However, neon tetras are schooling fish. So, you need to keep them in at least a group of 6-8. They will not school in a 3-gallon tank or a group of 2-4. 

But if you’re sure you want to keep them in a 3-gallon tank, you have to make sure you stay on top of water parameters. A 3-gallon tank will be a lot more temperamental than a 20-gallon tank. 

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