How Many Rasboras in a 5, 10 & 20 Gallon Tank? | Aquascape Addiction

How Many Rasboras in a 5, 10 & 20 Gallon Tank?

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Here are the essential housing space requirements for Rasboras, and answer the common question of how many of these fish you can house in a 5, 10 and 20 gallon tank.

How Many Rasboras in a 5, 10 & 20 Gallon Tank?

Rasboras are fan favorites among aquarium hobbyists, and for good reason, because they are bright and colorful, with strong personalities to match their appearance. Just like all aquarium fish, you need to house them correctly and in the right tank size.

So, How Many Rasboras in a 5, 10 and 20 gallon tank? Technically speaking, 1 Rasbora needs 4-5 gallons of space, so you could fit 1 fish in a 5 gallon tank.

However, these fish are schooling fish and should not be kept alone, at bare minimum they should be kept in pairs (2 at the very least) with schools of 5 or 7 being the recommended minimum.


  • In a 5 gallon tank, the answer is 0. While you can technically house 1 Rasboara fish it’s not recommended since these fish should not be alone.

  • In a 10 gallon tank, you can house 2 Rasboras (this is the bare minimum, though we wouldn’t recommend it).

  • In a 20 gallon tank, you can house 5 Rasboras (this is what we consider to be the minimum since they are a schooling fish).

Bottom line = Get a bigger tank of 20 gallons plus, so you can house at least a school of 5 Rasboras or consider housing a different type of fish.

Rasboras – A Quick Overview

A Harlequin Rasbora fish

The Rasbora is also known as the Spartacus fish, and yes, there are a few different types of rasboras out there.

The most popular and common type of Rasbora to have in a home aquarium is known as the Harlequin Rasbora or the red Rasbora. This fish originates in Southeast Asia, mainly from Thailand, Sumatra, Singapore, and Malaysia.

These are some fairly small fish which usually grow to a maximum length of 2 inches. Males and females are about the same size, but males tend to have a large patch of black on their bodies than females, plus the section that joins the anal fin is more rounded on males than females.

Rasboras are omnivores and are not overly picky, they are egg layers as opposed to live bearers, and they feature a medium difficulty care level.

They are not overly easy to care for, but also not overly difficult. Let’s now move on and talk about rasbora minimum tank size and some related facts as well.

Rasboras Minimum Tank Size

So the minimum tank size for a Rasbora, particularly for a harlequin Rasbora, is 4 gallons. Now, you might be used to the basic rule of thumb at each inch of fish should have 1 gallon of tank space. We have often advocated a larger tank, with 2 gallons of water being ideal for every inch of fish.

For a 2 inch Rasbora, this would mean a tank of 4 gallons at least, but most pros will recommend a tank of at least 5 gallons per each rasbora, as they are very active swimmers that like to have a lot of space.

What you need to know here is that Rasboras are schooling or shoaling fish, which means that they do not do very well alone. It is recommended to keep these fish in schools of at least 5 to 7 fish.

However, if you need to, it is ok to have only 2 of them, although definitely not ideal. Therefore, technically speaking, if you have 2 Rasboras, which you should (at the very least), the minimum tank size is going to be 10 gallons.

How Many Harlequin Rasboras Should I Get?

The very minimum requirement for housing Rasboras is to keep them in pairs. However, realistically, the bare minimum is not the same thing as the ideal.

Ideally, you want to have at least 5 to 7 Rasboras to make them feel at home. These are schooling fish that feel safe in numbers.

This is how they survive in the wild. It’s a simple numbers game. The larger a Rasbora school is, the lower the chances of any one individual being eaten by a larger predatory fish. If you have adequate space for them, the more the merrier.

Other Rasboras Housing Requirements

Let’s quickly go over some other Rasbora housing requirements, just so you know what you need to put in the tank and what kind of water conditions Rasboras need.

1. Water Parameters

The first thing to consider here is that Rasboras require the water temperature to be between 73 and 82 F (23 to 28 C). This means that in all likelihood, you will need an aquarium heater to keep the water warm enough for these fish.

Moreover, in terms of the pH level, Rasboras need to have this between 6.0 and 7.5. Also, in terms of water hardness, a level at or under 12 dGH is best.

2. Filtration

Harlequin Rasboras are pretty hardy fish, but this does not mean that they should not have clean water.

Realistically, no matter the type of fish, you always want to have an aquarium filter that engages in all 3 major forms of filtration, with these being mechanical, biological, and chemical filtration.

Also, in terms of flow rate, a 10 gallon tank should have a filter that can process at least 30 gallons of water per hour.

Although these fish are pretty good swimmers, they generally live in fairly still and calm waters, so try to keep water movement down.

3. Lighting

In terms of lighting, this is not all that important. Rasboras often live in fairly murky, still, and swampy waters with lots of plant cover from above.

However, that said, you do still want to have a basic aquarium light to provide them with a bit of illumination, just to mimic a natural habitat with a normal solar cycle.

These fish also like lots of plants in their tank, and you will need a half decent light to support plant growth.

Related: 15 ideal tank mates for Harlequins.

4. Oxygenation

Unless your fish tank is packed to the brim with lots of fish and minimal plant life, you really should not need an air pump or an air stone.

However, if you want to ensure that your Rasboras are as healthy and as happy as can be, a bit of extra oxygenation definitely won’t hurt.

5. Substrate

Rasboras live in environments that have sandy or gravel substrates, usually a mix of both, plus some natural earth thrown into the mix. Here, you can use either gravel or sand as substrate.

However, personally, we would recommend using gravel over sand. The reason for this is because gravel is not as messy to deal with and it does not tax filters as much as sand.

Moreover, Rasboras to enjoy heavily planted tanks, and gravel is much better for planted tanks than sand.

On a side note, we would recommend getting dark gravel, black if possible, as it will really make the colors on your Rasboras pop out. 1 to 1.5 inches of gravel at the bottom of the tan is sufficient.

6. Plants

The other thing you will want to put in your Rasboras tank are lots of live plants. Rasboras like live plants to provide them with cover and protection.

Here, you do want to stick to live plants that are predominantly found in Southeast Asia, or in other words, where Rasboras occur naturally.

You do want to avoid plastic and silk plants, as they tend to look worse than real plants, and they really don’t offer any of the benefits which live plants bring to a fish tank.

We have covered some good plant suggestions on a separate article here.


The bottom line is that when it comes to Rasboras, they should ideally be kept in schools of 5 with a minimum tank size of 20 gallons. At the very least, although not really recommended, 2 Rasboras can be kept in a 10 gallon tank.

Remember, these are schooling fish that find safety and comfort in numbers, so having 1 all on its own is absolutely not an option.

Photo Credit: Peter Maguire @ Flickr