A customer once showed us a beautiful 150 cm aquarium and asked:
“Is this big enough for my arowana? It is only 20 cm now.”
For the fish standing in front of us that day, probably.
For the same fish several years later, that was a different question.
Arowanas are often purchased as juveniles, which makes undersized aquariums look surprisingly spacious. But these are long-bodied, powerful surface swimmers. Depending on species and conditions, an adult can reach 60 cm or more .
That changes the way the aquarium should be selected.
For an arowana, tank size should be calculated around adult movement — not juvenile body length.
What Tank Size Does an Arowana Need?
There is no universal minimum because species, adult size and tankmates vary. But for many adult arowanas, especially Asian arowana, a useful long-term starting point is an aquarium approximately:
| Tank Dimension | Practical Starting Range |
|---|---|
| Length | 180–200 cm or more |
| Width | 70–90 cm or more |
| Height | 60–80 cm |
| Approximate Volume | Often 750–1,400+ liters |
For particularly large fish or arowanas kept with substantial tankmates, 200–240 cm or longer may make more sense.
Notice that width matters almost as much as length.
An arowana needs enough space to turn comfortably. A 60–70 cm adult fish inside a narrow aquarium may technically “fit,” but every turn becomes restricted.
This is why buying by liters alone can be misleading.
Fish don't swim in liters. They swim in dimensions.
Don't Make the Tank Taller Just to Make It “Bigger”
Suppose two aquariums contain similar amounts of water.
One gains volume through additional height. The other provides more length and width.
For an arowana, we would usually value the additional horizontal swimming area more.
This also has an engineering benefit.
Increasing aquarium height increases hydrostatic pressure on the glass, particularly toward the bottom of the panel. A taller aquarium may therefore require thicker glass, stronger bracing and more demanding structural calculations without giving the fish proportionally more useful swimming space.
At Ruibit, this is one reason we discuss fish size and aquarium proportions before glass thickness is finalized .
The animal and the structure are connected.
Filtration Should Be Sized for Feeding, Not Just Water Volume
A large predatory fish produces substantial waste.
So an arowana aquarium needs effective mechanical filtration to capture solids and enough biological media to support the bacteria processing ammonia and nitrite.
For larger installations, a sump is often the practical choice.
It allows mechanical media, biological filtration, return pumps, heaters and other equipment to be organized outside the display tank.
But sump size alone does not guarantee good filtration.
When Ruibit engineers an arowana system, we also consider expected feeding load, fish biomass, water flow through the media and maintenance access.
A huge biological chamber with poor flow is still a poor biological filter.
What Equipment Does an Arowana Tank Actually Need?
The core equipment is relatively straightforward:
Mechanical filtration removes feces, uneaten food and suspended debris.
Biological filtration provides surface area for nitrifying bacteria.
Return pump moves water through the filtration system and helps maintain circulation.
Heater and temperature controller maintain suitable, stable tropical conditions where heating is required.
Aeration can provide additional oxygen support, especially with heavier stocking.
Lighting should provide a consistent day/night cycle without repeatedly startling the fish.
UV sterilization is optional but can be useful for water-clarity management in some large systems.
Automatic top-off (ATO) can simplify evaporation management when a sump is used.
And there is one component we would never treat casually:
a secure cover.
The Lid Is Life-Support Equipment
Arowanas jump.
They can react suddenly to movement, noise, lighting changes or activity around the aquarium. A large adult fish striking an inadequate cover is very different from a small community fish jumping from an open tank.
The lid should therefore be secure while still allowing practical feeding and maintenance.
For custom Ruibit arowana tanks, we prefer to consider the cover, lighting and access openings together rather than adding a lid after the aquarium has already been built.
Good design prevents the problem instead of improvising around it.
A Large Arowana Aquarium Is Also a Structural Load
A 1,500-liter aquarium contains approximately 1,500 kg of water .
That is before adding the glass, cabinet or frame, sump, equipment and decoration.
As dimensions increase, glass thickness, panel deflection, silicone joints, bracing, stand construction and floor loading become part of the aquarium decision.
This is the point where “buy a bigger tank” stops being complete advice.
The aquarium has to be bigger safely .
Design for the Fish You Will Have in Five Years
When choosing an arowana aquarium, don't begin with the question:
“What tank can fit in this space?”
Start with the adult fish.
Estimate its mature length. Give it sufficient turning width and swimming length. Then design filtration around its waste load, equipment around the filtration, and the structure around the final weight of the complete system.
A 20 cm juvenile makes many aquariums look large.
That illusion doesn't last.
FAQ
Q: Can koi live in a home aquarium?
A: Yes, but only if the aquarium is very large and properly filtered. For long-term care, koi are usually better suited to ponds or large custom tanks.
Q: What size aquarium does one koi need?
A: A practical long-term starting point is about 250 gallons for one koi. More koi require much more water and filtration.
Q: Can I keep baby koi in a small tank?
A: Only temporarily. Juvenile koi can outgrow small tanks quickly, so plan an upgrade before buying them.
Q: What is the most important equipment for koi?
A: Strong biological filtration and aeration are the most important. Koi produce heavy waste and need stable oxygen-rich water.
