Fish comparison
Cardinal Tetra vs Threadfin Rainbowfish
How the Cardinal Tetra and Threadfin Rainbowfish compare on care, size, water and temperament, and which fish suits your tank.
By Mike ElmiraUpdated
TL;DR, Cardinal Tetra vs Threadfin Rainbowfish
The Cardinal Tetra and the Threadfin Rainbowfish come up together a lot when people are choosing a fish, and they are close enough to weigh side by side. Both are happy somewhere around 24 to 27 °C and pH 6.5 to 6.5, so a single tank can suit either one. Neither is harder than the other to keep, so the choice comes down to look and stocking rather than skill. If tank space is tight, the Threadfin Rainbowfish needs less room to feel settled; give the Cardinal Tetra the nod when you have the litres to spare.
Group compatibility overview
Good fit
Workable as-is, only minor advisories to plan around.
1 warning · 4 notes
Temperature
- Cardinal Tetra23–27 °C
- Threadfin Rainbowfish24–30 °C
pH
- Cardinal Tetra4.5–6.5
- Threadfin Rainbowfish6.5–7.5
Hardness
- Cardinal Tetra1–6 dGH
- Threadfin Rainbowfish5–15 dGH
What to plan for
- Narrow pH overlapTarget pH is 6.5–6.5. Test weekly; use buffered substrate or remineraliser to keep it stable.
- Cardinal Tetra schools, stock at least 8You've planned for 1 cardinal tetra. Cardinal Tetra need a group of at least 8 to feel safe and shoal naturally, below that they're stressed and lose colour. Dial up the count, or remove the species.
- Threadfin Rainbowfish schools, stock at least 6You've planned for 1 threadfin rainbowfish. Threadfin Rainbowfish need a group of at least 6 to feel safe and shoal naturally, below that they're stressed and lose colour. Dial up the count, or remove the species.
- No bottom teamNo bottom-dwelling fish or shrimp. A small group of corydoras or a shrimp colony picks up leftover food and keeps detritus in check.
- 67% of your fish swim in the midHeavy concentration in a single zone. Spreading stocking across all three levels makes the tank read fuller for the same bioload.
Full attributes
Every parameter, side by side| Parameter |  FishCardinal TetraParacheirodon axelrodi |  FishThreadfin RainbowfishIriatherina werneri |
|---|---|---|
| Category | Fish | Fish |
| Origin | Upper Orinoco and Rio Negro basins | Northern Australia, southern New Guinea |
| Family | Characidae | Melanotaeniidae |
| Temperature | 23–27 °C | 24–30 °C |
| pH | 4.5–6.5 | 6.5–7.5 |
| Hardness (dGH) | 1–6 | 5–15 |
| Flow rate | Low | Low to Medium |
| Min tank | 75 L | 60 L |
| Adult size | 4–5 cm | 4–5 cm |
| Difficulty | 3 / 5 | 3 / 5 |
| Lifespan | 4–6 yrs | 3–4 yrs |
| Diet | Omnivore | Micropredator |
| Water column | Mid | Mid to Top |
| Schooling | Yes | Yes |
| Plant safe | Yes | Yes |
| Shrimp safe | Mostly (may eat shrimplets) | Yes (adult shrimp) |
Frequently asked questions
Direct answers to the questions search engines and AI assistants surface most often about this species.
Can you keep Cardinal Tetra and Threadfin Rainbowfish together?
Yes. Their temperature and pH ranges overlap around 24 to 27 °C and pH 6.5 to 6.5, so one set of water conditions keeps both comfortable. Match group sizes and cover the usual planted-tank basics and they share a tank fine.
Which is easier to keep, the Cardinal Tetra or the Threadfin Rainbowfish?
They sit at the same care level, both middle-of-the-road, so neither is the obvious beginner pick. The decision is really about the look you're after.
Do Cardinal Tetra and Threadfin Rainbowfish need the same water?
Close to it. Aim for 24 to 27 °C and pH 6.5 to 6.5 and you're in the shared sweet spot for both. Full ranges are in the table above.
What's the main difference between the Cardinal Tetra and the Threadfin Rainbowfish?
Space. The Cardinal Tetra wants about 75 litres minimum and the Threadfin Rainbowfish around 60, so tank size can settle it.