How many Harlequin rasboras in a 10-gallon tank?

In this post, we will discuss the topic “How many Harlequin rasboras in a 10-gallon tank” and all steps of setting up a Harlequin rasbora aquarium. We will also suggest some fish species other than Harlequin rasboras to occupy a 10-gallon tank.

How many Harlequin rasboras in a 10-gallon tank

A 10-gallon tank can fit 2 or 3 Harlequin rasboras. Nevertheless, as they are shoaling fish, we strongly do not recommend this tank size. 

Harlequin rasboras usually grow no more than 1.75 inches. However, they can reach up to 2 inches long. Due to the Harlequin rasboras extremely active behaviour, our recommendation is to have 2 gallons of water per inch of Harlequin rasboras. Accordingly, 1.75 inches Harlequin rasboras would necessitate approximately 3,5 gallons of water.

10-gallon tanks are still considered nano tanks. Thus, it is very important to choose the inhabitants very carefully. A 10-gallon tank is one of the best tank sizes for learners. It allows hobbyists to gain some practice.

What you should know about Harlequin rasboras 

Harlequin rasboras are very amicable fish commonly found in home aquariums. Their looks and characters are what makes them admirable.

They have an extraordinary bright colouration design with a pink to orange background.

They are not demanding fish. However, they need to be kept in groups once they are schooling fish. A general recommendation is a group with at least 5 individuals. Although, they can thrive in smaller groups.

Their life expectancy is around 8 years if well cared for. They are small fish that measure 2 inches maximum. 

Setting a Harlequin rasbora tank 

Aquarium conditions are crucial for fish welfare. Harlequin rasboras do not have complicated needs to obey as they are little maintenance fish.

Water parameters

Water temperature in a Harlequin rasbora tank should be between 72 and 82 degrees Fahrenheit. Thus, it is fundamental to use a heater with a good controller in the tank. pH levels are recommended to be between 6 and 7.8 and water hardness less than 15 KH is ideal.

Tank size

The tiniest possible tank size for Harlequin rasboras is a 10-gallon tank. It is possible to raise a couple of Harlequin rasboras in it, although our recommendation is to go for bigger tanks.

However, it is still recommended larger tanks to keep larger groups. These fish are shoaling fish that enjoy being part of bigger groups. Thus, the bigger the room, the happier the fish. The usual rule for Harlequin rasboras is 2 gallons of water per inch of fish.

Water filtration system

Filtration equipment in a Harlequin rasbora tank should run in the 3 major manners: chemical, biological, and mechanical. These fish prefer slow-moving waters, and so, do not enjoy strong currents.

Plants & Substrate

A well-planted environment is better for the Harlequin rasboras. However, in small and nano tanks, this should be done very carefully to still provide some space to the fish and not overcrowd the tank.

For substrate, consider a mixture of sand and gravel. This will resemble their natural habitat and make them feel better and less stressed.

10-gallon tank dimensions

A regular 10-gallon tank dimension is 20 x 10 x 12 inches. However, it is likely to find many other arrangements and dimensions. The tank general weight when filled is around 110 lbs.

Other fish for a 10-gallon tank

When considering fish species for a nano tank, such as a 10-gallon one, it is crucial to keep in mind the fish species typical behaviours, such as temperament and social needs. Species that must be in large schools must be avoided, as or the tank would become crowded or the animals unhappy and stressed.

Setting Harlequin rasboras in a 10-gallon tank is not our core suggestion. This is because they are shoaling fish that do better in groups with a minimum of 5 individuals. Thus, we considered some other fish options for a nano tank with 10-gallon space that would do better than Harlequin rasboras.

Celestial Pearl Danio (Celestichthys margaritatus)

The Celestial Pearl Danios are low maintenance fish. They can grow only to 1 inch and are very peaceful. Thus, they are ideal fish for a 10-gallon tank. They are also very bright with gorgeous colours, which make them very admired among hobbyists.

They prefer tanks with plenty of plants and hiding spots. Their schools should have a minimum of 5 individuals and their general rule is 1 inch of fish per water gallon. Thus, it is possible to foster up to 10 Celestial Pearl Danios in a 10-gallon tank.

Pygmy Corydoras (Corydoras pygmaeus)

The Pygmy Corydoras are quite tiny catfish. They are very peaceful and should also be raised in schools of around 8 individuals. Similarly to the Celestial Pearl Danios, the Pygmy Corydoras also enjoy having hiding spots and vegetation around.

In a 10-gallon tank would be possible to keep up to 10 individuals. They are quite sensitive. Thus, it is important to keep all the water parameters well controlled.

Guppies (Poecilia reticulata)

Guppies are a good call for novice aquarists. They demand little maintenance effort. They breed very easily and thus, you should keep a single-gender in your 10-gallon tank. Otherwise, it could become overpopulated very easily. It is possible to raise around 10 Guppies in a 10-gallon nano tank.

Betta Fish (Betta splendens)

Betta fish are also very common picks for freshwater nano tanks. They have very attractive colours and looks and can come in many different shapes and colours. 

Betta fish should be kept as the unique individual of the species in a 10-gallon tank. Snails and shrimp will make nice tank mates for a Betta fish and give a nicer look to the tank. It is strongly recommended to raise your Betta fish in a well-planted tank with hiding spots.

Least Killifish (Heterandria formosa)

The Least Killifish is a perfect choice for a 10-gallon tank. They are ideal to raise in communities with loads of shrimp and snails. They are very tiny fish that measure from 0.8 to 1.4 inches. Thus, it is possible to keep around 15 Least Killifish in a 10-gallon tank.

They are active middle-layer swimmers. Thus, they require a more complex environment, with plants and structures from them to swim around and explore.

Dwarf Pencilfish (Nannostomus beckfordi)

The Dwarf Pencilfish is also a tiny fish species. They grow up to 1.5 inches only and are a good call for beginner aquarists, and do not require too much maintenance. It is possible to keep around 5 to 8 Dwarf Pencilfish in a 10-gallon tank.

10-gallon tank community combinations

If you cannot decide which species you want to keep in your 10-gallon

tank, here are some community combinations with fish and non-fish species that would fit perfectly into your nano tank:

–    1 Male Betta + 5-10 Cherry Shrimp;

–    8 Pygmy Corydoras + 1 Female Betta;

–      10 Least Killifish + 5-10 Cherry Shrimp;

–      8 Pencilfish + 5-10 Ghost Shrimp;

–      10 Celestial Pearl Danios + 1-2 Nerite Snails;

Tips for a 10-gallon tank

–       Set a routine of water change – this will guarantee low levels of ammonia and nitrites;

–     Go with a good filtration system no matter what the tank size is;

–     Do not overfeed the fish and do not overstock your tank – contaminant levels are harmful to fish;

–     Keep the fish species requirements and behaviours in mind – this will guarantee your fish wellbeing.

–   Plants, substrate and décor take space in a tank – it may be required

to recalculate your tank population once these features are set.


In this post, we discussed “How many Harlequin rasboras in a 10-gallon tank” and all steps of setting up a Harlequin rasbora aquarium. We also suggested some fish species other than Harlequin rasboras to occupy a 10-gallon tank.

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 10-gallon tank

Can Harlequin rasbora live in a 5-gallon tank?

No, once they are schooling fish, they require to be in groups. However, a 5-gallon tank would only fit 1 Harlequin rasbora, which makes this size of tank less than ideal.

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

If you have a 10-gallon tank, you can only house 2 or 3 Harlequin rasboras. They are very active middle-layer swimmers and thus, require 2 gallons of space for each inch of fish.

What are the standard dimensions of a 10-gallon tank?

The standard dimension for a 10-gallon tank is 20 x 10 x 12 inches and weighs around 110 lbs when filled.

How big Harlequin rasboras get?

Harlequin rasboras can grow a maximum of 2 inches. However, they are, in general, 1.75 inches long.

What tank size do Harlequin rasboras need?

A Harlequin rasboras pair or trio need at least a 10-gallon tank. However, it is recommended to keep them in larger tanks, as they prefer being in groups of at least 5 individuals.

Can Betta fish live with Harlequin rasboras?

Yes, Betta fish and Harlequin rasboras make great tankmates. They get along very easily and live peacefully.


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.

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