How Many Guppies In A 20 Gallon Tank?

Male guppies tend to be up to 1.4 cm long, whereas female guppies can be 2.4 cm long. So, how many guppies can we have in a 20-gallon tank? In this article, we will discuss all of it.

As a general rule, we can keep 10-14 guppies in a 20-gallon tank, depending on their sizes. However, make sure not to overcrowd your tank, as it can affect your guppy health. Also, to prevent guppies from excess breeding, consider adding male or female guppies only or more male than female guppies.

There are various factors to look at before deciding to keep numbers of guppies in a 20-gallon tank. So let us get more deeply into it.

How many guppies to keep in 20 gallon tank?

ParticularsNo of Guppies
Male Guppies ( 0.6 to 1.4 inches)10-12
Female Guppies ( 1.2 to 2.4 inches)5-7
Both Male And Female Guppies5-8
This table shows how many guppies we can keep in a 20-gallon tank.

Keeping the no of guppies in a 20-gallon tank entirely depends on the sizes of the guppies. Male guppies can vary from 0.6 inches to 1.4 inches, whereas female guppies can be from 1.2 inches to 2.4 inches.

If you are planning to keep all male guppies, then you can have 10-12 guppies in your 20-gallon tank, and in the case of female guppies, you can keep 8-10 guppies.

A guppy keeper can keep both male and female guppy on an average of 5-8 guppy in a 20-gallon tank.

No of male and female guppies to keep in 20 gallon tank?

The best way of knowing precisely the no of guppies to keep in a 20-gallon tank is by following the one-inch per on gallon rule.

One inch per one gallon of water rule is classified as Keeping 1 inch of fish per one gallon of water, which means in a 20-gallon tank, we can keep up to an average of 8 to 10 guppy.

In a 20 gallon tank, we will not be able to fill 20 gallons of water because some space will be covered by a heater, Soil, Filter, and other decors like natural plants.

If you plan to keep male guppies, you can keep an average of 10-12 guppies as they can get up to 1.4 inches in size.

If you plan to keep female guppies, you can keep an average of 5-7 guppies as they can get up to 2.4 inches in size.

If you are a beginner, then it will be good for you to start with keeping fewer guppies than having a pretty large number of guppies in the very starting.

I will recommend not to keep more than ten guppies in starting as it will help you to establish your tank nicely, and you will be able to maintain good care of your guppy fish.

Other tankmates we can keep with guppy in 20 gallon tank?

An owner should take care of many things before adding other tankmates in their guppy tank, like:

  1. The water condition should be the same for both the other fish and guppy
  2. The tankmates you are planning to add should not be aggressive.
  3. The food types of the tankmates should be similar to the guppy.
  4. The sizes of other tankmates should be the same as guppies, as the one with a bigger size can see your guppy as food. 

Here are some fishes which seems to fulfill the above requirement:

  1. Molly Fish
  2. Cory Catfish
  3. Gourami Fish
  4. Angelfish
  5. Platy Fish
  6. Rasbora Fish

These are some of the fishes you can keep with your guppy as their tankmates.

Also read: Can Guppy Fish Live With Angelfish?

Do the gender of the guppies matters?

Gender plays a crucial role in choosing the no of guppies to keep in a tank.

People with no experience always make a mistake by looking at male and female guppies as the same and with no difference.

The one who is experienced in fishkeeping can easily differentiate between male and female guppies.

Female guppies tend to be bigger than male guppies as female guppies have curvier and rounder bodies, whereas male guppies seem to be slender and longer in body shape.

As discussed above, male guppies can be 1.5 inches in size, whereas female guppies can be up to 2.5 inches.

Male guppies look more colorful than female guppies, especially in the tale area of male guppies.

Gender plays a vital role as the sizes of the guppies differ according to their gender.

What if the tank is crowded with too many guppies?

A tank with too many guppies can result in serious issues. Guppies are a schooling species and need more space to live comfortably, and they too like to live in freshwater.

Too many guppies in a tank can create problems like:

  1. Lack of space for guppies to live comfortably.
  2. The tank will get dirty very fast, which can make your fish sick.
  3. Your guppy can come under stress because of not getting enough space.
  4. Your guppy can get aggressive due to stress.
  5. More guppies in a tank mean more ammonia present in the tank, which can be very toxic for your guppies.
  6. The Filter present in the tank will not be able to clean it because of the overcrowded guppies, resulting in the bad water condition. 

An owner should make sure not to keep more than ten guppies in the case of male guppies and more than eight guppies in the case of female guppies.

If you plan to have both male and female guppy, you have to care for breeding problems.

Male guppies and female guppies in the same tank will breed and give babies, making your tank overcrowded. So, you can either donate the babies or sell them to the pet shop or separate them and keep them in another tank.

Also read: What To Do If My Guppy Is Stressed?

Can we keep more guppies in 20 gallon tank?

Many of us like to have more fish in a tank as the tank with overcrowded fish looks very beautiful, so we try to ignore the 1 inch per 1-gallon rule.

Keeping more fish in a 20-gallon tank can be possible if:

  1. Change 30% to 50% of the water every week.
  2. Add more live plants to your tank.
  3. Feed your guppy on a minimal basis; feed them once every other day.
  4. Use a good internal or external filter. 
  5. Use a special substrate for your aquarium.
  6. Adding good bio filter media to your filter will be beneficial. 

Water changes and maintenance

A more crowded tank with guppies will make the water dirty very quickly. An owner should make sure to clean the water regularly.

I will recommend changing the 30 or 50 percent of water weekly. A good filter can keep the water clean in an overcrowded guppy tank.

An owner has to make sure to clean the filter media too. Do not wash the filter media with aquarium water only; never use tap water to clean the filter.

Washing the filter media with tap water will result in chlorine killing all the good bacteria. A filter media should also not remain dry for a long time as that will kill all the beneficial bacteria too.

Add more live plants to your tank

I recommend having a live planted aquarium. I have live aquatic plants in all of my fish tanks, and they only don’t look so beautiful but also are helpful in many ways.

Live aquatic plants help keep the water clean by consuming the toxins produced by the fish waste, and also plants use these toxins for their growth.

Before planning to have a live planted aquarium, some things are essential for you to know:

  1. Natural aquatic plants need light to grow. Therefore, an owner should make sure to provide the plant’s light at least for 5-6 hours a day. Without light, your plants will die quickly, and also this will pollute the water.
  2. Your plant will need nutrients from time to time, for which we can use an aquarium plant fertilizer that will provide them the nutrients and help keep them healthy. 
  3. You can add nerite snails in your tank, as they will help eat all the dead plants and feed on algae. Adding nerite snails is not that important but is an ideal option for beginners. 

These are the plants you can add to your guppies tank:

  1. Amazon sword
  2. Watersprite
  3. Dwarf Sagittaria
  4. Guppy Grass
  5. Java Ferns
  6. Vallisneria nana
  7. Duckweed
  8. Giant Duckweed
  9. Amazon Frogbit

Also read: Does Guppy Eat Plants?

Feed your guppies on minimal basis

It is essential for beginners to know that guppies can eat all day long as they are always hungry.

Overfeeding your guppies can result in fish disease, and also it will pollute the water.

You can feed your adult guppy food every other day as they don’t need too much food, and also doing this will keep your guppy healthy also, the water will not get polluted.

Don’t provide your guppies food all at once; first, offer them a small lot of food and when you see that they have eaten it all, then repeat the process.

Also read: Can Guppy Die From Overfeeding?

Internal or external filter

An aquarium with overcrowded guppies will need a more powerful filter than the usual 20-gallon tank filter.

Buying a bigger internal filter with a high flow rate will help you keep more guppies in a 20-gallon tank.

Getting an external filter is much better as using it will remain vacant the space which the internal filter takes, and you can increase the water level of your tank in this way.

Also read: Do Guppies Need Filter?

Use a special substrate

In the case of a substrate, gravel is the most common substrate people use in their aquarium.

Gravel does not help in the cleaning process of water and takes up space only in the aquarium. An owner has to make sure to vacuum the gravel every time whenever you change the water.

There are lots of aquarium gravel cleaners available online, and also you can find them in the market.

If you want to replace gravel, there are many substrates present which is good for your aquarium. You can go for Seachem Flourite as it will help break down the fish waste by developing nitrifying bacteria.

Add good bio filter media to your filter

A good filter media is essential for your aquarium with overcrowded guppies.

In an aquarium with overstocked guppies, only a regular sponge filter will not do the work; you will need a good biological filter media, which will help provide enough surface area to the good bacteria for decomposing the harmful toxins like ammonia.


You can know how many guppies you can keep in a tank by following the one-inch fish per one gallon of water rule. For example, in a 20-gallon tank, you can keep an average of 10-12 guppies, depending on their sizes.

The gender of the guppy does matter as the male guppies are smaller in size than the female guppies.

If you want an overcrowded guppy tank, then there are a few things you can do, like using a more oversized and powerful filter, adding live plants, providing minimal food to your guppies, and using a good biological filter media.

Reference: ResearchGate, NCBI

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