Compatibility Overview
Cardinal Tetra and Discus are generally not recommended to be housed together. The issues listed above — whether water parameter incompatibility, predation risk, or aggression — create conditions where one or both fish are likely to suffer harm or chronic stress.
| Factor | Cardinal Tetra | Discus | Verdict |
|---|---|---|---|
| Temperature | 73–82°F | 82–88°F | ⚠️ 82–82°F (narrow) |
| pH Range | 4.5–7.0 | 5.0–7.0 | ✅ 5.0–7.0 |
| Temperament | peaceful | semi | ⚠️ Monitor |
| Adult Size | 1.5 in | 8 in | ❌ 5× difference |
| Min. Group | 6+ | 5+ | See below |
| Min. Tank Size | 100 gallons (for both species) | — | |
✅ Compatibility Positives
❌ Incompatibility Reasons
Species Profiles
Cardinal Tetra — Paracheirodon axelrodi
Brilliant red-and-blue schooling fish from the Rio Negro. Prefers soft, acidic, warm water — a natural companion for discus.
→ Full Cardinal Tetra care guide
Discus — Symphysodon spp.
The 'king of the aquarium' — beautiful but demanding. Requires very warm, soft, acidic water that excludes most community fish.
Frequently Asked Questions
Can Cardinal Tetra live with Discus?
Generally not recommended. Cardinal Tetra and Discus are generally not recommended to be housed together. The issues listed above — whether water parameter incompatibility, predation risk, or aggression — create conditions where one or both fish are likely to suffer harm or chronic stress.
What tank size do I need for Cardinal Tetra and Discus together?
A minimum of 100 gallons is recommended for keeping Cardinal Tetra and Discus together. A larger tank improves water stability and reduces territorial conflict.
What temperature suits both Cardinal Tetra and Discus?
82–82°F (narrow)
Is a Cardinal Tetra aggressive toward a Discus?
Cardinal Tetra is peaceful and Discus is semi. Minimal temperature overlap (82–82°F) — difficult to satisfy both species simultaneously.