How Many Neon Tetras In A 20-Gallon Tank? 10 or 30?

Dec 19, 2021

How Many Neon Tetras In A 20-Gallon Tank?

A properly stocked neon tetra is a work of art. It’s a conversation starter. Watching the explosion of blue and red colors, coupled with geometric schools, is really a fantastic sight to behold. A 20-gallon tank for neon tetras is really a good starting point if you’re testing the waters in the hobby. So that begs the question – how many neon tetras in a 20-gallon tank?

How Many Neon Tetras In A 20-Gallon Tank?

You can add anywhere between 10 to 30 neon tetras in a 20-gallon tank. I know that’s a vast range, but let me explain. 10 is a safe number to begin with. But if you’re an experienced fishkeeper confident enough with overstocking, 30 is perfectly doable. 

Several hobbyists have successfully kept and recommended keeping 30 neon tetras in a 20-gallon tank, from what I have found. 

However, note that the stocking number also boils down to the kind of tank you have. If you have a 20-gallon long tank, you can definitely raise more neons than what a 20-gallon high tank would allow due to its bigger footprint. 

There are a couple of rules that hobbyists follow to decide the stocking number. There’s the debatable “one inch per gallon” rule and the more liberal “12 square inches of surface area for every inch of the body”.

So, let’s find out what the stocking numbers would look like if we followed these rules. 

The 1 Inch Per Gallon Rule 

As I said above, this rule is quite debatable. That’s because it doesn’t consider the space taken by decors, plants, and substrate. It also completely ignores the fish’s height during calculation. 

However, the general notion is that this rule can be applied for fish smaller than 3 inches. For larger fish, it is entirely bogus. I mean, imagine adding a 12-inch oscar to a 12-gallon tank. 

On average, neon tetras reach 1.5 inches (4 cm) in length. unBut for the sake of this calculation, let’s assume they are 1.75 inches long (4.45 cm).  

So, a 20-gallon tank would house 11.42 (20/1.75) neon tetras. You can either round it off to 11 or 12. 

The 12 Square Inches For Every Inch Rule

This rule was given by acclaimed fishkeeper and author Dick Mills in his famous book You And Your Aquarium. This is also the rule that many experienced fish hobbyists swear by. 

They believe that we must consider the surface and floor area of the tank to calculate the stocking number. And that’s because the oxygen exchange happens at the top, and the good bacteria process fish waste at the base. 

I’ll explain how we can calculate the stocking number based on this rule in 3 simple steps. 

Step 1

Calculate the surface area of the tank by multiplying the tank’s length and width (L x W). 

Step 2

Calculate the total inches of fish the tank can hold by dividing the surface area by 12 (surface area / 12). 

Step 3

Calculate the total number of fish the tank can hold by dividing the answer from step 2 by the fish’s height. (total inch of fish the tank can hold/fish’s height). 

Now, let’s calculate the stocking numbers for a 20-gallon high tank and a 20-gallon long tank, respectively. 

For a 20-gallon high tank, 

The tank’s dimensions: 24” x 12” x 16” (L x W x H)

Let’s assume the neon tetras are 1-inch tall to stay on the safe side. But from what I have read, their average height clocks in at just 9-12 mm (0.35-0.47) inches. 

Let’s calculate the tank’s surface area first. 

L x W = 24” x 12” = 288

Now, let’s find out the total inches of neon tetras a 20-gallon high tank can hold. 

Surface area/12 = 288/12 = 24

Finally, let’s calculate the total number of neon tetras a 20-gallon high tank can house. 

Total inches the tank can hold / average height = 24/1 = 24

So, when we follow the ’12 square inches for every inch of the fish’s body’ rule, we can house around 24 neon tetras in a 20-gallon high tank.

Now, let’s calculate for a 20-gallon long tank.

20-gallon tank’s long tank’s dimensions: 30″ x 12″ x 12″ (L x W x H)

Surface area = L x W = 30” x 12” = 360

Total inches of fish a 20-gallon long tank can hold: 30 

Total number of neon tetras a 20-gallon long tank can hold = 30/1 (fish’s assumed height) = 30

So, a 20-gallon long tank can hold about 30 neon tetras. 

However, note that the answer heavily depends on factors like how often you’re willing to perform water changes, the number of decors and plants you have in the tank, and your fishkeeping experience. 

So, enough math for today – let’s have a look at what real hobbyists have to say. 

I have collected some answers on the subject left by hobbyists on different platforms. I hope they will help you make a practical and more informed decision. 

Let’s have a look! 

Recommended Readings!

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How Many Neon Tetras In A 5-Gallon Tank? Honest Answers!

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

How Many Neon Tetras In A 10-Gallon Tank? With Bettas And Guppies?

How Many Neon Tetras In A 20-Gallon Tank? Real Answers By Real People!

“I would say 20-30 would be fine depending on the filtration mechanism and your maintenance schedule.”

“30-40 of neon tetras would not be out of the question – particularly in a 20-gallon long tank – as long as you have proper filtration, perform weekly water changes, and maintain cleanliness.”

“It boils down to you and your willingness to do the work involved in raising X number of tetras. You can play it safe with only a dozen or go big with 40, but then have lots of work ( water changes, filter cleaning, etc.). 40 neons in a long tank would be a beautiful sight to see – but lots of work.”

“Will the tank be planted? Neon tetras have a very small bioload. 30-40 in a 20-gallon tank will be fine and not much work if your tank is heavily planted.”

“I would say keep about 17. Yes, I know it’s an odd number, but it’d make the school look better. I got around 20, and it worked out great. Just make sure you get them from a place you trust so you don’t end up with 20 dead fish after one day.”

You can see that housing 20-30 of them in a 20-gallon tank is not impossible if you’re willing to put in some elbow grease routinely. However, if you’re just dabbling in the hobby and don’t have much experience or confidence, it’s best to stick to a dozen! 

How Many Neon Tetras In A 20-Gallon Tank With Betta?

Credits: Maxxum (Creative Commons license)

It’s not uncommon for people to keep bettas in tanks smaller than 3 gallons. However, these fish should at least be housed in a 5-gallon tank for them to live comfortably. 

So, let’s assume the betta needs 5 gallons. You are then left with 15 gallons for neon tetras. When we apply the ‘one inch per gallon’ rule, you can house around 8.57 (15/1.75) neon tetras. 

You can round it off to 9. 

So, you can house around 1 betta and 9 neon tetras together in a 20-gallon tank. If you were to house 2 bettas, you could have 6 neon tetras. 

It’s important to know that bettas and neon tetras don’t really make the best candidates to keep in a 20-gallon tank. And that’s because bettas are pretty aggressive and territorial fish. They need plenty of space to feel comfortable. 

And neon tetras may respond to a betta’s aggression by nipping its beautiful, long fins. Yes, neon tetras have a knack for nipping fins. 

But as long as all fish have enough space to swim around and ‘claim’, you can house them together without any complication. 

How Many Neon Tetras And Guppies In A 20-Gallon Tank?

Male guppies can reach up to 1.5 inches (1 inch on average). Females are usually bigger than males, reaching 2.4 inches (2 inches on average). 

Let’s assume the fish’s average length is 2 inches to leave some room for mistakes. 

So, if you allocate 10 gallons for guppies, you can house 5 (10/2) of them in a 20-gallon tank. 

Now, you have 10 gallons remaining for the neon tetras. So, you can house 5.7 (10/1.75) neon tetras in a 20-gallon tank. You can round it off to 6. 

Therefore, the final answer is you can house 5 guppies and 6 neon tetras in a 20-gallon tank if you allocate 10 gallons each for both species.

How Many Neon Tetras Should You Keep For Them To School? 

Credit: Ananda Raj Kumar (Creative Commons license)

Neon tetras are schooling fish that move together in thousands in the wild. In the tank, you should at least keep them in a group of 6 if you want to observe their unique schooling behavior. 

Why Do Neon Tetras School?

Schooling is an innate nature for neon tetras. The primary reason behind this is to protect themselves from their enemies. Naturally, predators find it a lot easier to chase and devour a fish swimming all alone instead of trying to cut out a single fish from a big group. 

Another reason is that this helps the tetras defend their territory better. No wonder the mean bullies will think twice before confronting an angry school of hundreds of fish. 

The third reason is open to debate, but it’s widely believed that swimming close together helps to reduce friction and allow fish to conserve energy while swimming. 

And finally, the fourth reason is that swimming in schools helps tetras forage better. A hundred sets of eyes are definitely better than 1 or 2 sets in finding potential food and prey. 

How To Maintain A 20-Gallon Aquarium? 

A 20-gallon aquarium makes a great starting point if you’re new to the fishkeeping hobby. It’s neither too small nor too big.

But at the end of the day, an aquarium, no matter how big, is still a relatively small amount of water compared to natural water bodies. 

On top of that, it’s a closed system. 

Therefore, you need to take good care of the aquarium throughout your fish’s lifespan to give them the best life possible. 

Below, we will discuss how you can maintain a 20-gallon neon tetra aquarium in sections. 

The Frequency Of Maintenance 

It’s neither desirable nor practical to clean every nook and cranny of an aquarium daily. Also, it’s not recommended to clean everything simultaneously as this can swiftly demolish the good bacteria colony. 

If you disrupt the good bacteria colonies too much, it will hamper the tank’s nitrogen cycle – resulting in a spike in ammonia and nitrite levels. 

Things You Should Do Daily 

First thing in the morning, conduct a visual check of the tank to ensure the filtration system is running at its full strength, the lights are functioning okay, and the right temperature is maintained. 

Also, do a headcount and check if all the fish appear healthy and normal. The best time to count is when you’re feeding them. They’ll be easier to observe and count at this time. 

And once the fish are done eating, remove the leftovers, so the water stays clean for a longer time. If you notice that there’s always some food left uneaten, maybe it’s time to cut back on the quantity. 

If you notice anything unusual, I’d recommend keeping a note of it somewhere so you can study the pattern and work on it. 

Here’s a quick summary of the paragraph:

  • Check filtration equipment 
  • Check the temperature 
  • Count and observe fish
  • Remove uneaten food 
  • Top off the water level
  • Note concerns in a logbook

Things You Should Do Weekly/ BiWeekly 

There’s no one rule set in stone when it comes to performing water changes. Some hobbyists strongly advocate changing waters every week, while others believe that doing so every few weeks will suffice too. 

So, you can perform water changes weekly or biweekly, depending on your stocking number. When adding new water to the tank, make sure the new water is treated, and if possible, aged. 

The parameters of the replacement water should closely match that of the tank’s original water. 

But there are certain things you should do before you change the water. Changing the water should be the last task you perform. 

The other task you should perform once every week or two weeks is cleaning, of course. Start by wiping down the outside of the tank’s surface with a non-ammonia, tank-safe cleanser. 

Also, gently shake the plants to dislodge the debris. Next, scrape the insides of the glass to get rid of the algae build-up. 

Now, wait for a while – 5 to 10 minutes – so all the debris and gunk settle down to the bottom. Then gently siphon the substrate to get rid of everything. 

And finally, perform a partial water change. 

Here’s a quick summary of the paragraph. 

  • Wipe down the outside surfaces 
  • Shake off debris from plants 
  • Scrape the inside glass
  • Siphon the substrate 
  • Perform a partial water change 

Things You Should Do Monthly 

You should perform water parameter tests at least once monthly to ensure nothing harmful is brewing. The four most important parameters to monitor are pH, nitrate, nitrite, and ammonia. 

And for that, we recommend using the API’s Freshwater Master Kit. 

Using a liquid-based test is more reliable than strips. 

If your tank has an algae problem, don’t forget to test the phosphate levels as well. 

You need to test the water parameters before performing a water change. 

You can also prune the plants, so they don’t outgrow your tank. 

Next, perform all the things mentioned in the weekly/biweekly list.

And don’t forget to save a bucket of water taken out from the tank to perform filter maintenance. 

If you use exhaustible media like zeolite or activated carbon, replace them monthly. 

As for mechanical media, rinse it using the water saved from the water change. But if the mechanical media seems too clogged, simply replace it. 

But you need to retain the part of the media to prevent losing all of the beneficial bacteria colonies. 

Here’s a quick summary of the paragraph. 

  • Perform water tests 
  • Trim plants as needed 
  • Perform the weekly/biweekly tasks 
  • Change filter media

Things You Should Do Periodically

Besides the routine maintenance tasks, there are a couple of things you should do on an ad-hoc basis. For instance, these include changing the light bulbs as needed – once every six months or 1 year. 

You should also inspect the air pump tubing and the filter tubing if you have a canister filter. Clean the canister filter intake with the help of a filter brush. 

And if you have live plants, fertilize them if needed. 

Here’s a quick summary of the paragraph:

  • Replace light bulbs 
  • Inspect and maintain tubing 
  • Clean the filter intake 
  • Fertilize plants 

Frequently Asked Questions 

What Are The Best Tankmates For Neon Tetras In A 20-Gallon Fish Tank? 

Ideal tank mates for neon tetras in a 20-gallon fish tank would be:

  • Endler’s guppies 
  • Snails 
  • Platies
  • Barbs
  • Mollies 
  • Glofish 
  • Zebra danios 
  • Hatchetfish
  • Harlequin rasboras 
  • Chili rasboras
  • Dwarf gouramis 
  • Corydoras catfish
  • Zebra loaches 
  • Otocinclus catfish 
  • Kuhli loaches 

How Many Neon Tetras In a 29-Gallon Tank? 

If we were to follow the ‘1 inch per gallon’ rule, we could comfortably house 16-17 neon tetras in a 29-gallon tank assuming the tetra’s mean height is 1.75 inches. 

And if we were to apply Dick Mill’s rule of allocating 12 square inches of surface area for every inch of the fish’s body, we could house 30 neon tetras in a 29-gallon tank, assuming they’re 1-inch tall.

How Many Neon Tetras In A 10-Gallon Tank?

When we divide 10 by 1.75, we get 5.7. And we can round it off to either 5 or 6. So, you can house 5-6 neon tetras in a 10-gallon tank. 

That’s a pretty decent number! That’s also the minimum number of neon tetras you can keep to observe their schooling behavior. 

How Many Neon Tetras In A 5-Gallon Tank?

When we divide 5 by 1.75, we get 2.8. And we can round it off to 3. So, you can add 3 neon tetras in a 5-gallon tank. However, keep in mind that these fish need to be kept in a group of 6 or more for them to feel comfortable. 

Final Words: How Many Neon Tetras In A 20-Gallon Tank?

A 20-gallon tank is a perfect size for a beginner. It’s not small enough to not have any room for mistakes nor big enough to be overwhelming to tend.

A 20-gallon fish tank can house anywhere between 10-30 neon tetras. I know 10-30 is a pretty wide range for an answer. But let me explain. 

If you’re a beginner and are trying to find your feet in the hobby, stock 10-12 fish. And once you are confident enough about your experience and knowledge, you can stock up to 30 fish! 

But remember, the higher the number of fish, the higher the demand for maintenance. 

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rohit gurung author at urbanfishkeeping

About Rohit Gurung

My never-ending love and fascination with Aquascaping started when I received a red-eared turtle for my 10th birthday.

Apart from researching and writing, I spend hours gazing at my 3 turtles. And yeah, I bask alongside them too.