How Many Neon Tetras In A 20 Gallon Tank?
Care & Breeding

How Many Neon Tetras In A 20 Gallon Tank?

An accurately stocked neon tetra is a complete artwork. Observing the beautiful explosion of blue and red colors, mixed with geometric schools, is definitely a mind-blowing sight to behold. Basically, a 20-gallon tank for neon tetras is an ideal starting point but then the question rises how many neon tetras should be there in a 20 gallon tank?

How Many Neon Tetras In A 20 Gallon Tank?

You can add anywhere between the range of 10 to 30 neon tetras in a 20-gallon tank. That might sound like a very huge range, but basically, 10 is a safe number to start with. But if you are a skilled aquarist then you might be assertive enough with overstocking, in this situation 30 is perfectly doable. 

Many of the aquarists have been successful in keeping and they also suggest keeping 30 neon tetras in a 20-gallon tank. 

But the main thing to note is that the number of stockings also boils down to the type of tank you have. If you are having a 20-gallon lengthy tank, then yes you can definitely raise more tetra neons than what a 20-gallon high tank would allow because it has a bigger footprint. 

Also, there are certain rules that should be followed by aquarists in order to decide the stocking number. There is the popular “one inch per gallon” rule and also there are the more liberal “12 square inches of surface area for every inch of the body”.

How Many Neon Tetras In A 20 Gallon Tank
How Many Neon Tetras In A 20 Gallon Tank

The 1 Inch Per Gallon Rule 

In this situation, this rule might be quite arguable. This is because it actually does not consider the space which is taken by decorations, plants, and even substrate. This rule also entirely ignores the height of the fish during the process of calculation. 

But basically, the general notion is that this rule can be applied to fish which is smaller than 3 inches. But For larger fish, this rule doesn’t apply and can be a big disaster.

On average, basically, the neon tetras can reach up to 1.5 inches which are 4 cm in length. But for this particular calculation, we can assume they are 1.75 inches long which is approximately 4.45 cm

So, then a 20-gallon tank would be able to house 11.42 which is 20/1.75 neon tetras. You can also round it off to 11 to 12. 

The 12 Square Inches For Every Inch Rule

This rule was introduced by commended fish keeper and also author Dick Mills in his popular book “You And Your Aquarium” also this rule is liked by many skilled fish aquarists. 

In this rule, they say that we should think about the surface and also the floor area of the tank in order to calculate the number of stockings. And this is because the oxygen exchange is happening at the top and the good type of bacteria process fish waste at the bottom of the tank. 

Here we will explain how you are able to calculate the stocking number based on this famous rule in 3 easy steps. 

Step 1

Initially, you must Calculate the surface area of the tank. This can be done by multiplying the tank’s length and width which is L x W.

Step 2

In the second step, you should Calculate the total inches of fish the tank can hold. This can be done by dividing the surface area by 12 which in the formula will be surface area / 12.

Step 3

In the last step, you are going to Calculate the total number of fish the tank can hold by dividing the answer you got from step 2 by the fish height. Which is the formula will be the total inch of fish the tank can hold/height of fish.

Now we are going to calculate the stocking numbers for a 20-gallon high tank and a 20-gallon tank in length respectively. 

For a 20-gallon high tank, 

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

Now let us consider that the neon tetras are 1 inch tall by staying on the safer side. But from most of the information, their basic average height clocks in at just 9-12 mm which in inches is 0.35-0.47 inches. 

Now we are going to calculate the tank’s surface area first. 

(Length * width) L x W = 24” x 12” which will be 288

Now we will find out the total inches of neon tetras a 20-gallon high tank is able to hold. 

Surface area/12 = 288/12  which will be 24

In the final step, we are going to calculate the total number of neon tetras a 20-gallon high tank is able to house. 

The total inches the tank can hold divided by average height = 24/1 which will be 24

So, when we are following the ’12 square inches for every inch of the fish body rule, we are able to house 24 neon tetras in a 20-gallon high tank.

Now we will calculate for a 20-gallon long tank.

20 gallon tank’s long tank’s dimensions: 30″ x 12″ x 12″ (Length x Width x Height)

Surface area = Length x Width= 30” x 12” which will be 360

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

So after this calculation, the Total number of neon tetras a 20-gallon long tank can hold is 30/1 (fish assumed height) which is 30 

So far we came to the conclusion that a 20-gallon long tank can hold about 30 neon tetras. 

But you should know that the final answer mostly depends on important factors like how often you want to perform water changes, the number of decorations and plants you are having in your home tank, and also your fishkeeping experience. 

How Many Neon Tetras In A 20 Gallon Tank
How Many Neon Tetras In A 20 Gallon Tank

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

It’s not something uncommon for people to keep bettas in tanks that are smaller than 3 gallons. But these fish must be housed in a 5-gallon tank for them to live happily and stress-free. 

Now, let’s consider the betta needs 5 gallons then You are left with 15 gallons for neon tetras. Now if we are applying the ‘one inch per gallon’ rule, you will be able to house around 8.57 which is 15/1.75 neon tetras. 

You can also round it off to 9. 

Now you are able to house around 1 betta and 9 neon tetras jointly in a 20-gallon tank. But in another condition, If you were able to house 2 bettas, you can have 6 neon tetras. 

It’s very important to know that bettas and neon tetras are not the ideal partners to keep in a 20-gallon tank. And that’s because bettas are pretty truculent and territorial fish. They require plenty of space to feel comfortable and stress-free. 

And in a result neon tetras may respond to a betta’s truculence by biting on its beautiful, long fins. Yes, you heard it right!! neon tetras have the ability of nipping fins. 

But as long as all fish have sufficient space to swim around then you can keep them jointly without any issues or complications.

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

Male guppies can actually reach up to 1.5 inches and 1 inch on average. Female guppies are usually big in size than males reaching 2.4 inches and 2 inches on average.

Now let’s consider the fish’s basic average length is 2 inches as we are leaving some room for mistakes. 

So now if you allot 10 gallons for guppies, then you are able to house 5 which is 10/2 of them in a 20-gallon tank. 

Now the remaining is  10 gallons for the neon tetras. So in this situation, you are able to house 5.7  which is 10/1.75 neon tetras in a 20-gallon tank. You can also round it off to 6. 

So the final answer is you can house 5 guppies and then 6 neon tetras in a 20-gallon tank if you are doing 10 gallons each for both of the species.

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

Neon tetras are known as schooling fish that move jointly in thousands in the wild. In your tank, you must at least keep them in a group of 6 in order to observe their distinctive schooling behavior. 

Why Do Neon Tetras School?

Schooling is an inborn nature for neon tetras. The initial reason behind this is to safeguard themselves from their enemies. Basically, predators find it easier to chase and enjoy a fish swimming alone instead of trying to chase a single fish from a huge group. 

Another reason which is found is that this helps the tetras protect their territory better. 

The third reason is arguable, but also highly believed that swimming very closely together is a great way of reducing friction and allowing fish to conserve energy while they are swimming. 

And finally, the last and fourth reason is that swimming in schools helps tetras feed in a  better way. A hundred sets of eyes are definitely the best option than 1 or 2 sets in hunting for potential food and prey. 

How Many Neon Tetras In A 20 Gallon Tank
How Many Neon Tetras In A 20 Gallon Tank

How To Maintain A 20-Gallon Aquarium? 

A 20-gallon aquarium is a great initial point if you are new to fishkeeping life. It’s not too small and not too big for you.

But obviously, in the end, it’s an aquarium, and no matter how big it is, it is still actually a tiny amount of water compared to natural water areas. 

So as a result, you have to take proper care of the aquarium throughout your fish’s lifespan to give them the best life possible so they live in your aquarium stress-free and happy.

The Frequency Of Maintenance 

It’s neither advisable nor practical to clean the inside and outside of an aquarium every day. Also, it’s not suggested to clean everything simultaneously as this can quickly destroy the good bacteria area. 

If you mix or change the good bacteria colonies too much, it will hamper the tank’s nitrogen cycle which will result in a spike in ammonia and also nitrite levels. 

How Many Neon Tetras In A 20 Gallon Tank
How Many Neon Tetras In A 20 Gallon Tank

Things You Must Do on a Daily basis

The first thing you should do in the morning is to do a visual checkup of the tank to make sure the filtration system is running at its complete strength, the lights are working perfectly fine, and the right temperature is going on. 

You must do a headcount and check if all the fish look healthy, calm, and normal. The ideal time to count is when you are giving them food. At that time They will be much easier to observe.

And once the fish are done eating their food, then you must remove the leftovers, so the water stays clean and fresh for a longer period of time. If you observe that there is always some food left uneaten, then that’s a sign that it’s time to cut back on the quantity of food.

If you notice anything abnormal, then we would suggest keeping a note of it somewhere so you can observe the pattern every day and simultaneously work on it. 

Here’s a bullet point summary of the above paragraph :

  • Must Check the filtration system 
  • Check the temperature 
  • Count and observe fish every day
  • Remove uneaten food and leftovers
  • Note your observations in a logbook

Things You Should Do Weekly

There is not one rule set when it comes to water changes in your tank. Some aquarists strongly suggest changing tank water every week, while others recommend that doing so every few weeks is also sufficient.

So as a result you can do water changes weekly or in a few weeks, which basically depends on your stocking number. When you are adding new water to the tank, then ensure that the new water is treated, and if possible, it must be aged. 

The parameters of the new water should be very closely matched with that of the tank’s original water. 

But there are a few things you must do before you change the tank water. Changing the tank water must be the last task you are going to perform. 

Some other task you must perform once every week or in two weeks is cleaning the tank. You should start by wiping down the outside of the tank surface with a non-ammonia, tank-safe cleanser to make it clean and hygienic.

Also, you should carefully shake the plants to remove the debris. The next thing you should do is to scrape the insides of the glass to get rid of the algae which build up in your tank. Then you must wait for a while for at least 5 to 10 minutes so all the dirt settles down at the base. Then carefully and slowly siphon the substrate to get rid of all the dirt. 

And in the last stage, you should perform a partial water change. 

Things You Should Do on a Monthly basis

On monthly basis, you should perform water parameter tests at least once a month to make sure nothing dangerous is brewing. The four most important parameters in order to monitor our pH, are nitrate, nitrite, and ammonia. You should keep these parameters in mind while performing water parameters tests

And in that case, we suggest you use the APIs, Freshwater Master Kit. 

How Many Neon Tetras In A 20 Gallon Tank
How Many Neon Tetras In A 20 Gallon Tank

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

Some best tank partners for neon tetras in a 20-gallon fish tank would be:

  • Endler’s guppies 
  • Snails
  • Glofish 
  • Zebra danios 
  • Hatchetfish
  • Barbs
  • Mollies


A 20-gallon water tank is an ideal size for a new aquarist. It’s not too small to not have any room for mistakes and not too big enough to be overwhelming to handle.

You can house a  20-gallon fish anywhere between 10-30 neon tetras. Basically, if you are a novice and are trying to find your feet in this world, then stock 10-12 fish. And once you are confident enough about your experience with the fish and you have sufficient knowledge, then you can also stock up to 30 fish! 

But one thing you must remember, the greater the quantity of fish, the higher demand for maintenance. 

To read more about Fish caring and breeding or more about different types of fish visit our website

How Many Neon Tetras In A 20 Gallon Tank?
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