How many Harlequin rasboras in a 20-gallon tank?

In this post, we will discuss the topic “How many Harlequin rasboras in a 20-gallon tank” and all steps of setting up an Angelfish aquarium.

How many Harlequin rasboras in a 20-gallon tank

A 20-gallon tank can fit up to 5 Harlequin rasboras. Harlequin rasboras can grow up to 2 inches long and are highly active swimmers. For this reason, the general rule for Harlequin rasboras is 2 gallons of water per inch of Harlequin rasboras in length. 

Harlequin rasboras 

Harlequin rasboras are the most popular rasbora variety. They can easily be found in freshwater home aquariums. They are the favourite rasboras due to their bright colouration and great personalities.

These fish require low effort for maintenance and do not require any expertise, only minimum knowledge. They are schooling fish that prefer to be in groups with a minimum of 5 individuals. Their schooling swimming behaviours are graceful and eye-catching.

Harlequin rasboras life expectancy is between 5 and 8 years. These fish can grow up to 2 inches long. They have a pink or orange diamond-shaped body.

Male and female Harlequin rasboras have minor sexual dimorphism. The black patch is usually larger in males with a rounded look on the bottom of the triangular shape. Females have a very straight patch shape. Size can also be a gender indicator. Usually, female Harlequin rasboras are larger than males. 

Natural habitat

Harlequin rasboras are original from Southeast Asia, predominantly from Malaysia, Singapore, and Thailand. These fish naturally occupy several different habitats, from swamp forests to slow-moving rivers. 


Harlequin rasboras are omnivores. In the wild, they eat anything that fits their mouth.

In a tank, it is possible to use small flakes and pellets as the basis of the diet. A nutritional supplement is strongly encouraged to keep a balanced diet. 

Some supplements can be dry food with some live prey. Bloodworms, Daphnia, and Brine shrimp are good options for Harlequin rasboras feeding


Harlequin rasboras are extraordinarily peaceful fish. They do not nip to other fish fins nor perform aggressive behaviours.

Due to their small size, they can become prey to larger fish. For this motive, it is recommended not to consider larger fish as tankmates.

The first company you should consider for Harlequin rasboras is other Harlequin rasboras. This is due to their very social behaviours. 

Additionally, if you do not have enough space for the Harlequin rasboras school, it would be important to move them to another tank before getting any tankmates.

Some of the best Harlequin rasboras fish and non-fish tankmates are listed below.

–       Harlequin rasboras;

–       Neon and Cardinal Tetras;

–       Corydoras;

–       Plecos;

–       Danios;

–       Dwarf Gourami;

–       Zebra Loaches;

–       Mollies;

–       Platies;

–       Cherry Barbs;

–       Hatchetfish;

–       Guppies;

–       Snails;

–       Shrimp (Cherry shrimp).

Harlequin rasbora tank requirements

Tank conditions are extremely important for fish health. Harlequin rasboras are very common in community tanks. For this reason, tank requirements need to be clear, once it is needed to match the conditions required to test the fish compatibility.

In general, Harlequin rasboras are not demanding fish to keep. Thus, you should not have any behavioural issues related to tank and water conditions.

Water parameters

Harlequin rasboras require temperatures ranging between 72 and 82 degrees Fahrenheit. Thus, it is important to keep a heater and a thermostat in the tank.

Also, pH levels should vary between 6 and 7.8 and water hardness between 2 and 15 KH is ideal.

Tank size

The minimum tank size for Harlequin rasboras is 10-gallon. It is possible to keep a small group of 5 Harlequin rasboras as well as enough substrate, plants, and decorations.

The general rule for Harlequin rasboras is 2 gallons of water per inch of Harlequin rasbora.


This is not essential for Harlequin rasboras as they inhabit waters with lots of plant cover. Thus, keeping a basic aquarium light with a bit of illumination should be enough to mimic the Harlequin rasboras natural environment.

Water filtration system

Harlequin rasboras are classified as hardy fish. However, they still need to be kept in high quality and clean water. The ideal filtration system should work in the 3 major filtration schemes, biological, mechanical, and chemical.

Regarding flow rates, it is important to have a filter that can process 30 gallons of water per hour for a 10-gallon tank. However, keep in mind that Harlequin rasboras do not enjoy strong currents. Thus, keeping a slow-moving water system is recommended.


Harlequin rasboras naturally occupy areas with sandy and gravel substrate. Thus, the general recommendation is to mix both types of substrate. 

However, sandy substrate requires more care and attention. Therefore, for beginner aquarists, it is suggested to use gravel. Additionally, a darker substrate may give a better look to the tank, as it would contrast with the Harlequin rasboras colours. Rocks and driftwood can also make nice additions to Harlequin rasboras tanks.


Harlequin rasboras appreciate well-planted tanks. For this reason, it is recommended to keep plenty of live plants. Harlequin rasboras use the plants as hiding spots and cover for protection purposes. 

Also, it is recommended to provide some natural plants from the original habitat of the Harlequin rasboras. In other words, native plants to Southeast Asia.


In this post, we discussed “How many Harlequin rasboras in a 20-gallon tank” and all steps of setting up an Angelfish aquarium.

If you have any thoughts or doubts, feel free to drop us in a comment below!

Frequently Asked Questions (FAQs): How many Harlequin rasboras in a 20-gallon tank

How many Harlequin rasboras can you keep together?

Harlequin rasboras are schooling fish. Thus, they should be in groups of 8 to 10 individuals. However, bigger groups result in more beautiful displays.

How many Harlequin rasboras can I put in a 10-gallon tank?

If you have a 10-gallon tank, you could place up to 2 Harlequin rasboras in it. Harlequin rasboras are very active swimmers, for this reason, it is considered 2 gallons per inch of fish in length. 

How big do Harlequin rasboras get?

Harlequin rasboras can grow only up to 2 inches or 5 centimetres, and thus, do not require huge tanks.

Are Harlequin rasboras hardy fish?

Yes, Harlequin rasboras are classified as hardy fish. They do not fall sick frequently. Under adequate conditions and proper care, they can thrive easily.

How often should I feed Harlequin rasboras?

A school of Harlequin rasboras should be fed three times a day. Regarding the amount of food, they should eat completely within 3-4 minutes.

Can Neon Tetras live with Harlequin rasboras?

Yes, Neon and Cardinal Tetras are great Harlequin rasboras tankmates. They are all peaceful easy-going species that do well in the same parameters.


Stanton, L. 2021. How Many Rasboras Can You Have In a 5, 10 & 20 Gallon Tank?

Yang, A. 2020. Harlequin Rasbora Care: Size, Tank Mates, Breeding & More.

Stanton, L. 2021. 15 Best Tank Mates for Harlequin Rasboras (With Pictures).

Edmond, A. Harlequin Rasbora: Everything You Need To Know.