How many Harlequin rasboras in a 15-gallon tank?

In this post, we will discuss the topic “How many Harlequin rasboras in a 15-gallon tank” and all steps of setting up a Harlequin rasbora aquarium.

How many Harlequin rasboras in a 15-gallon tank

A 15-gallon tank can fit 3 or 4 Harlequin rasboras. However, as they are schooling fish, this is not the recommended minimum tank size. Harlequin rasboras usually grow no more than 1.75 inches. However, they can reach up to 2 inches long. 

The recommendation for Harlequin rasboras is to provide 2 gallons of space per inch of Harlequin rasboras. Thus, 1.75 Harlequin rasboras would require around 3,5 gallons of water.

Although it is still considered a small tank size, a 15-gallon tank is the best tank size for beginners. It allows first-trip aquarists to obtain some experience.

What you should know about Harlequin rasboras 

Harlequin rasboras are very popular peaceful fish. They are popular due to their remarkably bright colouration pattern and great temperament.

They do not require aquarium expertise as they are low effort fish to keep. Since they are schooling fish, the recommendation is to keep them in groups of at least 5 individuals. Although, they can live in smaller groups also. 

These fish can live for up to 8 years. Though, the average is 5. They are small fish that only grow up to 2 inches maximum. They have a rosy to ginger diamond-shaped body.

What to feed Harlequin rasboras with

Harlequin rasboras are omnivorous fish. They can be offered small flakes and pellets as the basis of the diet with animal items as nutritional supplementation, such as bloodworms and Brine shrimp.

Setting a Harlequin rasbora tank 

Tank requirements are significant for fish well-being. Harlequin rasboras do not have complex requirements to follow as they are low maintenance fish.

Water parameters

Harlequin rasboras require water temperatures between 72 and 82 degrees Fahrenheit. Thus, it is essential to use a heater and a regulator in the aquarium.

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

Tank size

The smallest tank size for Harlequin rasboras is 10-gallon. It is possible to keep a few Harlequin rasboras as well as substrate, some plants, and décor. 

However, we still recommend larger tanks to keep larger groups. These fish are schooling fish that require larger groups. Thus, the larger the tank, the happier the fish. The general rule for Harlequin rasboras is 2 gallons of water per inch of Harlequin rasbora.

Water filtration system

The recommended filtration arrangement for Harlequin rasboras should cover the 3 major schemes: chemical, biological, and mechanical.

Harlequin rasboras do not enjoy strong currents. Thus, keeping a slow-moving water system is recommended.

Plants & Substrate

Harlequin rasboras natural habitats have sand and gravel as a substrate. Thus, a mixed tank substrate would be ideal for these fish.

Harlequin rasboras appreciate heavily-planted tanks. For this reason, it is recommended to keep plenty of live plants for hiding spots and coverage for protection reasons. 

15-gallon tank dimensions

A regular 15-gallon tank dimension is 24 x 12 x 12 inches. However, it is possible to find several other shapes and measurements. The tank weight when filled is around 170 lbs.

Other fish for a 15-gallon tank

Setting Harlequin rasboras in a 15-gallon tank is not our first recommendation. This is because they are schooling fish that do better in groups of at least 5 or 6 individuals. Thus, you could opt for other awesome colourful fish that would do better in 15-gallon tanks than Harlequin rasboras.

It is recommended to avoid any fish larger than 2 inches and also territorial or aggressive ones.


Guppies are very colourful fish and give an extraordinary look to a fish tank. They are also schooling fish and grow to between 1 and 2 inches. They have a peaceful amicable temperament.

A 15-gallon tank would be enough to house 10 to 15 Guppies. However, keep in mind that Guppies breed very easily. Thus, this tank can become heavily populated in a short period.

Neon and Cardinal Tetras

Tetras refer to a group of fish species. Smaller ones such as Neon and Cardinal Tetras are awesome options for 15-gallon tanks. Their colours are extraordinary and bring an amazing look to your tank. They grow a maximum of 1.5 inches in length and live for 2 or 3 years.

They are peaceful and non-aggressive. Also, they do not perform any antagonistic behaviour. Due to their usual behaviour, the general rule for these fish is 1 gallon of water per inch of fish. Thus, it would be possible to keep around 10-12 small tetras in a 15-gallon tank.


Danios are also a good choice for a 15-gallon tank. They are also very pacific schooling fish. Additionally, they can come in a huge variety of colours and would make a splendid tank.

The general rule for Danios is 1 inch of fish per gallon of water. Thus, it is possible to house around 8 small Danios in a 15-gallon tank as they grow a maximum of 2 inches.

Cherry and Tiger Barbs

Cherry barbs, as their name suggests, have an awesome red colouration. They are the least aggressive species among the barbs. However, they are schooling fish that require having at least 5 individuals in a group.

These barb species grow to 2-2.5 inches on average, which means there could be around 6-7 individuals in a 15-gallon tank.

Dwarf Gouramis

Dwarf Gouramis are also very peaceful fish and usually do not perform any aggressive behaviour. These fish have an astonishing unique look and enjoy well-vegetated tanks.

They can grow up to 3.5 inches and the minimum tank size required for them is 15-gallon. Thus, it will be possible to house a pair of Dwarf Gouramis in this tank.


Platies or Platy fish are very peaceful and easy-going schooling fish. They appreciated well-planted tanks. 

Platies can grow up to 2.5 inches. However, they usually reach only 1.5-1.75 inches when adults, in captivity. Thus, a 15-gallon tank can house up to 8 platies. Their general rule is also 1 inch of fish in 1 gallon of water. 

Community combinations

If you cannot decide which species to keep in a 15-gallon tank, you may start considering community combinations. Below are some:

–       1 Dwarf Gourami + 5 Guppies (males) + 3 Mystery snails +4 Amano shrimp

–       5 Celestial Pearl Danios

–       1 Dalmatian Molly

–       1 Pearl Gourami


In this post, we discussed “How many Harlequin rasboras in a 15-gallon tank” and all steps of setting up a Harlequin rasbora 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 15-gallon tank

Do Harlequin rasboras nip fins?

Harlequin rasboras are not fin-nippers. It is very uncommon to observe this behaviour performed by Harlequin rasboras.

How many Harlequin rasboras can I put in a 20-gallon tank?

If you have a 20-gallon tank, you could place 5 or 6 Harlequin rasboras. Harlequin rasboras are very active swimmers, for this reason, the recommendation is to provide 2 gallons of space for each inch of fish.

Are Rasboras tropical fish?

Yes, Rasboras is a genus of around 45 species. They are all schooling tropical fish and belong to the Cyprinidae family. Most of the species are found in Asia. However, there are few found in Africa as well.

Can Harlequin rasboras live in hard water?

Harlequin rasboras require a water hardness level up to 12 dGh. Additionally, pH levels should be around 6-6.5.

Are all rasboras peaceful?

Yes, the Rasboras nature is peaceful. They can get along with several other fish species and make awesome community tank inhabitants.

Can you mix different Rasboras?

Yes, it is possible to mix different rasboras species. They will probably school together. In general, they limit other kinds of fish from their groups. However, they school with similar ones.


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.