30L Biorb: How Many Fish Can You House? | Aquascape Addiction

30L Biorb: How Many Fish Can You House?

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Here is a detailed guide on what kinds of fish you can house in your 30L Biorb tank and what types of fish are the best options for you. Including which you should avoid.

30L Biorb: How Many Fish Can You House?

Biorbs are pretty cool aquariums to have for at home. Yes, this is a brand name, and they are called Biorbs because they are round aquariums, kind of like fishbowls, but they come with filtration, lights, and other such things already included. However, you might be wondering what the Biorb 30 fish capacity is. In other words, how many fish can you house in a 30L Biorb?

Well, this is going to differ greatly based on the type of fish you want to keep inside of it. If you have Betta fish, you could only keep a couple in it. When it comes to smaller cichlids, you could fit a few. Tetra fish are very small, so you could fit a whole lot of those in in the Biorb 30.

Let’s go over the 30L Biorb in terms of how many fish it can house, based on different types of popular aquarium fish.

Fish Type How Many In A Biorb 30?
Tetra Fish 7 - 9
Betta Fish 1
Dwarf Gourami 1
Guppies 2
Pygmy Corydoras 3 females and 6 males

How Many Gallons Are 30 Liters?

Ok, one thing that we probably need to go over here is converting liters to gallons. Yes, the Biorb 30 is advertised in liters, and it is a 30 liter aquarium.

However, when we talk about how much room a fish requires, we usually always talk in terms of gallons, as do most others.

Therefore, it’s probably important for you to know that 30 liters equals approximately 8 gallons. Now that you know how many gallons one of these things can hold, we can move onto our next sections.

Keep The Filter, Plants & Substrate In Mind

Something that you do need to keep in mind when it comes to something like the Biorb 30 liter aquarium is that all of that space is not going to be reserved solely for fish. You have to consider the fact that there will also be a filtration unit inside of the aquarium, some plants, substrate, and possibly a bubbler too.

If you have a large centerpiece, as often comes with Biorbs, one that includes some plants, rocks, and a built in filtration unit, you have to subtract this from the overall tank volume that will be left for the fish.

Worst case scenario, this 30 liter or 8 gallon Biorb, with all of the filtration unit, plants, and rocks inside of it, may leave you with somewhere around 7 gallons of space for the fish themselves.

So, when it comes down to it, an 8 gallon Biorb has more like 7 gallons of space for fish, not 8. In terms of liters, this is roughly 26 liters of volume reserved for fish.

How Many Fish In 1 Gallon Of Water?

Now, we know that we said that how many fish you can fit into this 30 liter or 8 gallon Biorb really depends on the size of the fish, but there are some general guidelines for you to follow here. Generally speaking, the rule is that you want no more than 1 inch of fish per gallon of water.

Sure, you could push this a little bit, maybe 1.25 inches of fish per gallon of water, but absolutely no more than that.

Therefore, if you have a fish that is 1.25 inches long, it will require roughly 1 gallon of water volume to be healthy and happy with the amount of space it has.

However, do keep in mind that this is not the same for all fish species out there, especially more territorial ones which require more space to feel comfortable.

So, simply put, a Biorb like this, that realistically has about 7 gallons of space inside of it, can fit 7 inches of fish, or 8.75 inches worth of fish at the most.

So, if you have a small 1 inch neon tetra, this means that you can fit roughly 8 of them in this 39 liter Biorb. Let’s move on and talk a little more in depth in regards to particular aquarium fish species and how many of each you could possibly fit into this thing.

Best Fish For 30L Biorb Fish Tank

Let’s go over some of the most popular fish species that aquarium owners tend to buy, and then talk about how many of them you could fit into the Biorb 30.

Let’s keep in mind that here we are going with the more realistic 7 gallon measurement, because while it is an 8 gallon aquarium, the filter and decorations do take up a good deal of space.

Tetra Fish

a tetra fish

Tetra fish tend to be quite small, usually under 1 inch in length, usually around 0.75 inches in length.

This is a great fish to go with for the 1 gallon of water per inch of fish example. Based on this, in a Biorb 30 with 7 gallons of space, you could fit up to 9 tetra fish with ease.

If you want to give them a bit more space, only put 7 tetras in the Biorb 30.

Betta Fish

a betta fish

Betta fish are very cool. They look pretty, have big personalities, and are really not all that difficult to care for.

The minimum tank size for a betta fish is 2.5 gallons, but more like 3 - 5+ gallons if you really want it to be comfy. Technically speaking, you could therefore fit up to 2 betta fish in the same Biorb 30.

However its not recommended, do keep in mind that these fish are territorial and aggressive towards their own species, so realistically, a single betta fish in the 30L Biorb is what we recommend.

Dwarf Gourami

a dwarf gourami

Gouramis tend to be fairly decent sized fish, usually way to big to put in a tank like this. However, there are Dwarf Gouramis, which as you can probably tell by the name, is a smaller type of Gourami fish.

These guys require a minimum tank size of 5 gallons, which means that you can fit 1 of them into the Biorb 30 comfortably.


a guppy fish

The guppy is another type of fish that makes for a decent Biorb 30 candidate. These are small, colorful, and fairly peaceful fish that are easy to care for.

They do not like to be alone, so you will need at least 2 of them. Now, the rule of thumb here is that 3 guppies should have 10 gallons of tank space.

How many guppies in 30 litre biorb?

So, in a Biorb 30, with about 7 gallons of room on the inside, you could fit 2 guppies comfortably.

Pygmy Corydora

a pygmy corydora fish

Pygmy Corydoras make for another good candidate for the Biorb 30. These are fairly small and very colorful fish, usually topping out at about 1 inch in length.

These guys can survive and thrive in pretty small tanks, but they need to be in small schools, so keep that in mind. For 1 female and 2 males, around 2.5 gallons of water will suffice.

So, in this Biorb 30, you could potentially keep up to 3 females and 6 males, although it will be a little tight. A decent school of these fish usually requires about 10 gallons of water.

What About Goldfish?

Another common question we see is ‘how many goldfish in a 30 litre biorb tank?’, well the answer is none, the 30L biorb is way too small for Goldfish, they require much more space in order to be happy and healthy. For example, one fancy Goldfish requires at least a 20 gallon tank.


There we have it guys, how many fish you can fit into a Biorb 30 liter aquarium. Remember, while it is technically an 8 gallon tank, keep in mind that the decorations and filter are going to take up around 1 gallon, so realistically it is a 7 gallon tank.

There are various small aquarium fish which make for good Biorb 30 candidates, but to be fair, most fish will need more space than this.

Photo Credits: Tetra_Glowlight.jpg: gonzalovalenzueladerivative work: Kyknos [CC BY 2.0], via Wikimedia Commons

Jvarszegi [Public domain], via Wikimedia Commons

Marrabbio2 [CC BY-SA 3.0], via Wikimedia Commons

Birger A [CC BY-SA 3.0], via Wikimedia Commons