Cardinal Tetra and Koi Compatibility Overview
Cardinal Tetra and Koi are generally not recommended to be housed together. Koi is a cool-water fish and Cardinal Tetra is tropical, so the usable temperature range decides this pairing. The adult size gap creates a meaningful predation risk. Review the behavior and water details before deciding whether to attempt the pairing.
| Factor | Cardinal Tetra | Koi | Verdict |
|---|---|---|---|
| Temperature | 73โ82ยฐF | 50โ75ยฐF | โ ๏ธ 73โ75ยฐF (narrow) |
| pH Range | 4.5โ7.0 | 7.0โ8.5 | โ ๏ธ 7.0โ7.0 (narrow) |
| Temperament | peaceful | peaceful | โ Compatible |
| Adult Size | 1.5 in | 24 in | โ 16ร difference |
| Min. Group | 6+ | 2+ | See below |
| Min. Tank Size | 100 gallons (for both species) | โ | |
Compatibility Positives
Incompatibility Reasons
Species Profiles
Cardinal Tetra โ Paracheirodon axelrodi
Brilliant red-and-blue schooling fish from the Rio Negro. Prefers soft, acidic, warm water โ a natural companion for discus.
โ Full Cardinal Tetra care guide
Koi โ Cyprinus rubrofuscus
Large pond fish that require hundreds of gallons and cool water. Will eat any fish small enough to fit in their mouth.
Frequently Asked Questions
Can Cardinal Tetra live with Koi?
Generally not recommended. Cardinal Tetra and Koi are generally not recommended to be housed together. Koi is a cool-water fish and Cardinal Tetra is tropical, so the usable temperature range decides this pairing. The adult size gap creates a meaningful predation risk. Review the behavior and water details before deciding whether to attempt the pairing.
What tank size do I need for Cardinal Tetra and Koi together?
A minimum of 100 gallons is recommended for keeping Cardinal Tetra and Koi together. A larger tank improves water stability and reduces territorial conflict.
What temperature suits both Cardinal Tetra and Koi?
73โ75ยฐF (narrow) โ inside Cardinal Tetra's 73โ82ยฐF and Koi's 50โ75ยฐF.
Is a Cardinal Tetra aggressive toward a Koi?
The adult size gap creates a meaningful predation risk.
Related Compatibility Guides
Tank Size for Cardinal Tetra and Koi
Use the scenario that matches the actual group sizes and temperament you plan to keep.
| Scenario | Tank | When it applies |
|---|---|---|
| Minimum viable | 100 gal | Only for the recommended minimum groups, mature filtration, and close monitoring. |
| Recommended community | 150 gal | Adds territory, swimming room, and a safer buffer for behavior. |
| Low-conflict setup | 220 gal | Best when keeping larger schools or reducing territorial pressure. |