How Many Guppies Can You Keep in a 20-Gallon Tank?




how many guppies in a 20 gallon tank

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Peaceful and beautiful to watch, guppies are very popular aquarium fish that are highly sought after for their ease of care.

If you have a 20-gallon tank and want to keep guppies, knowing how many you can keep to prevent overcrowding is important.

Read on to find out!

How Many Guppies Can Live Comfortably in a 20-Gallon Aquarium?

This is one of the most common questions of any new guppy fish keeper. The general rule is no more than 20, but it depends on several factors.


The gender of guppies has an important effect on how many guppies you can keep in your tank.

Unlike other aquarium fish, male guppies are smaller than female guppies, so it shouldn’t be a problem if you plan to have up to 12 males. For females, keeping 10 or fewer in a 20-gallon fish tank is best.

Only Female Guppies

Female guppies range from 1.2 to 2.4 inches in size. A 20-gallon fish tank can hold around 8 to 10 female guppies.

Only Male Guppies

Male guppies range between 0.6 and 1.4 inches long. For males, 10-12 guppies can thrive comfortably in a 20-gallon guppies tank.

Mixed Gender Guppies

If you plan on keeping both males and females, keep a ratio of one to two, males to females. The ratio is important for a peaceful tank environment because males are more territorial than females. For a 20-gallon guppy aquarium, a proper ratio would be four males to eight females for 12.


The size of your fish is crucial when deciding how many you can fit in your tank. If you buy them young, you may not know how big they will grow versus buying full-grown adult guppies.

What If They Spawn?

If you decide to keep both males and females, there is a chance you will end up with babies. You won’t be able to keep the babies in the same aquarium, so you would have to buy another aquarium to keep them.

Separating males and females into different tanks can prevent this from happening in the future.

Can Guppies Overcrowd the Tank When They Mate?

Yes! Unfortunately, if you decide to keep a mixed guppy tank with males and females, and they mate, it can lead to an overcrowded aquarium.

Despite being nonviolent fish, guppies tend to eat their own offspring. Although why they do this is unknown, there are several possible reasons why including:

  • Female guppies eat their offspring to retain fat storage
  • To keep only strong offspring and eat the weak offspring
  • Female guppies can experience stress after birth, causing them to eat their fry.

To prevent this from happening, keep adults and fry apart until the offspring has grown.

Tank Maintenance Requirements

A 20-gallon tank with guppies is usually easy to maintain if there aren’t too many fish. Keep the water temperature between 72 to 80 degrees Fahrenheit and provide a balanced diet.


Your filter plays a vital role in the routine care for your fish. A good filter will have three stages:


The biological filter function takes care of ammonia produced by fish waste from uneaten food and decaying plants. It aids in beneficial bacteria growth, which turns ammonia into nitrite.


The mechanical filter acts like a sponge filter and removes large particles and debris from your tank to keep the water clean.


The chemical function helps to remove water contaminants in tap water, such as minerals, hard metals, and chemicals, and remove odors from your tank.

What Is the Rule for the Number of Guppies Per Gallon?

It is generally recommended to have an inch of fish per gallon. Adult guppies grow to around 1 to 2 inches, so you can keep one guppy per gallon of water.

What If I Have Too Many Guppies in the Tank?

Guppies are a typically small, low-care breed. However, that doesn’t mean that overcrowding the aquarium won’t cause problems.

There are many downsides to overcrowding a tank that can be detrimental to guppy health.

Uncomfortable Tank Space

Guppies are fairly active, so a tank size needs enough space for them to swim around. If the tank is overcrowded, guppies may begin to experience the following symptoms:


Guppies can become stressed when they don’t have enough space to swim freely. Stress has an impact on their immune system health and causes disease.


No matter the tank setup, there will be aggression when guppies are stressed. The male’s competitive nature can increase beyond normal levels due to more competitors being present.

More Waste

With more guppies, the number of waste increases, which can lead to bad water conditions and ammonia poisoning. Ammonia levels will rise due to bacteria build-up, and your filter won’t be able to keep up.

Less Oxygen

When too many guppies are kept in a tank, the amount of oxygen decreases. Decreased oxygenated water can lead to a weak immune system and cause them to develop unnaturally.

Who Make Good Tankmates for Guppies?

There are many compatible mates for guppies in a 20-gallon tank. Some of these include:

How To Setup the Ideal 20-Gallon Guppy Tank

Setting up a guppy tank is pretty simple as long as you follow some basic rules. Here’s how to do it:

Provide a Powerful Quality Filter

If you’re a beginner guppy keeper, using an external filter versus an under-gravel internal filter is best. Use a filter that can filter 100 gallons of water hourly to keep your aquarium balanced.

Choose Your Substrate

Once you’ve chosen your filter, you must choose and add your substrate.

Gravel is generally a common substrate people recommend for guppies. Around 3 inches at the bottom of the tank will do. Make sure to use aquarium-grade gravel to prevent contaminants from getting into your water.

how many guppies in a 20 gallon tank

Add water

Add water into your aquarium until your water level reaches half full. This way, you can place decorations and plants without overflowing the tank.

Adding Live Plants and Decorations to Your Aquarium

Introduce decorations, rocks, and plants to your tank deeply rooted in the gravel to offer hiding spots for guppies. Like many other aquarium fish, guppies love aquatic plants to hide in.

Ample plants can also help maintain aquarium water quality by removing toxins from the fish and providing oxygen back to the water.

Some natural plant options that are favorites of guppies include:

Add An Air Pump

Air pumps help to create water movement to open up the surface area to exchange gasses.

Add Your Water Heater

Guppies need a water heater because, like most aquarium fish, they need the correct water parameters to thrive. They live in temperate waters between 75 and 84 degrees.

Add Light

Guppies need light during the day, like most aquarium fish, so adding a light with a timer can help. Setting it for 8 hours will be ideal for your guppies’ light needs. They also need 8 hours of darkness daily.


A 20-gallon tank is well suited to keep guppies as long as you meet the requirements. A 20-gallon tank can hold more male guppies than females due to their size, but if you’re thinking of keeping both genders, just be prepared to mate and have a backup plan for when they do.

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