From the arowana corner of the Ruibit Aquarium factory, Foshan — where the display tank is 2.4 meters long for a reason — a customer walked in beaming about his deal.
"I got a baby silver arowana, 15 centimeters, and a 100-gallon tank," he said. "Everything I need, all at once."
We told him what he didn't want to hear: he had everything he needed for the fish he bought. Nothing he needed for the fish he'll have.
The fish you buy is not the fish you keep
Here's the counterintuitive part, and it's the whole article: arowana grow. They grow fast, they grow big, and they grow for years. That 15-centimeter baby will pass 30 centimeters in its first year. By year two, it's brushing 60. A silver arowana — the "cheap" one — keeps going to a meter or more. The fish you choose at the store is a hatchling; the fish you'll be keeping in five years is a completely different animal.
We call it the adult-size rule: size the tank for the adult, never for the baby. Every arowana disaster starts the same way — a beautiful juvenile, a reasonable-looking tank, and a timeline nobody did the math on.
The size reality: three numbers you can't argue with
- Adult length: Asian arowana (golden, red) reach 60–90 centimeters. Silver arowana reach 90–120.
- Growth rate: 20–40 centimeters in the first year. The juvenile phase is the shortest phase.
- Lifespan: 15–25 years. This is a two-decade commitment, not a purchase (see our 20-year rule for koi — same math, different fish).
That's why the single-fish minimum is 180–250 gallons, and it's the floor, not the goal. Below that, the fish doesn't die in week one — it dies of the small tank over years: cramped spine, stunted growth, a mouth that scrapes the glass. Slow, invisible, and entirely predictable.
Length × width, not volume
Here's what most size guides get wrong: for arowana, the volume is not the first number. The dimensions are.
Length: the tank must be at least 3–4 times the adult body length — 1.8 meters minimum for an Asian arowana, 2.4 meters for a silver. Arowana are surface patrol fish; they swim in long passes, all day, every day. A short tank is a treadmill.
Width: the number everyone forgets. An arowana needs 60–75 centimeters of width to turn around. Narrow tanks are where the famous deformities come from: a bent spine from years of tight turns, and "dropped eye" — the fish staring downward because the tank is too shallow in width for it to look forward. A narrow arowana tank is not a home; it's a corridor with a fish in it.
Depth: 60 centimeters of water is enough — arowana are top dwellers; the height of the tank matters far less than the length and width.
The equipment list: six things that matter
- The tank. 180–250 gallons minimum, long and wide, with the adult in mind.
- Filtration — a sump, not a canister. Arowana are big eaters with big waste. Run a sump with a large media chamber at 4–6 times the tank volume per hour. This is a sewage plant question, not a filter question (see our koi waste-plant rule — the same biology applies).
- A heater — mandatory. This is where arowana are the opposite of koi: they're tropical fish. 25–30°C, stable, year-round. A heater failure in winter is a stress event that takes weeks to undo.
- Lighting — soft, from above. Strong light and a reflective water surface train arowana to look down — that's the mechanics of dropped eye. Keep lighting gentle and indirect, and the fish keeps its eyes where they belong.
- A heavy lid — non-negotiable. Arowana are the jump champions of the aquarium world. They clear the rim when startled, and a lightweight lid won't stop a 60-centimeter fish. The heavyweight-lid rule: if you can lift the lid with one hand, the fish can lift it with its head.
- Bare bottom. No gravel, no sand. Arowana produce large, heavy waste — bare glass keeps it where the sump can find it.
The two-decade tenant
Here's the part nobody at the store mentions: an arowana is not decor. It's a tenant. It will live 15–25 years, outlast apartments, jobs, and relationships — and it needs the same tank the whole time. Moving a large arowana is a two-person operation and a trauma for the fish. The tank you buy today is the tank that fish will live in for the rest of its life.
That's why we give the honest advice to anyone with less than a 180-gallon footprint: don't buy an arowana. It's not a beginner fish (see our beginner guide — arowana sit in the "not for beginners" tier for a reason), and the "cheap" silver arowana is the worst trap of all: it's the one that grows past a meter, needs an 8-foot tank, and outlives the enthusiasm that bought it.
The patrol
Here's the scene that makes the big tank worth every liter. It's evening, and the 2.4-meter tank in the arowana corner is running quiet — sump humming, heater steady at 28°C. The arowana cruises the full length of the glass, turns in the wide water, and glides back. No cramped pivot. No scraping. Just the long, patient patrol of a fish that has room to be what it is.
That's the whole answer to the size question. An arowana doesn't grow into your tank. Your tank has to grow into it. Size for the adult — the length for the patrol, the width for the turn, the sump for the waste — and the fish you bought at 15 centimeters will still be the fish you keep at 80.
At Ruibit, we build arowana systems the same way every time: adult-sized footprint, sump at 4–6x, heavyweight lid, soft light. The formula never changes, because the fish never stops growing — and the tank that's right on day one is the tank that's still right in year fifteen.
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.
