Compatibility Overview
Discus and Koi 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 | Discus | Koi | Verdict |
|---|---|---|---|
| Temperature | 82–88°F | 50–75°F | ❌ No overlap |
| pH Range | 5.0–7.0 | 7.0–8.5 | ⚠️ 7.0–7.0 (narrow) |
| Temperament | semi | peaceful | ⚠️ Monitor |
| Adult Size | 8 in | 24 in | ⚠️ 3.0× difference |
| Min. Group | 5+ | 2+ | See below |
| Min. Tank Size | 100 gallons (for both species) | — | |
✅ Compatibility Positives
❌ Incompatibility Reasons
Species Profiles
Discus — Symphysodon spp.
The 'king of the aquarium' — beautiful but demanding. Requires very warm, soft, acidic water that excludes most community fish.
Koi — 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 Discus live with Koi?
Generally not recommended. Discus and Koi 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 Discus and Koi together?
A minimum of 100 gallons is recommended for keeping Discus and Koi together. A larger tank improves water stability and reduces territorial conflict.
What temperature suits both Discus and Koi?
No overlap
Is a Discus aggressive toward a Koi?
Discus is semi and Koi is peaceful. Discus requires tropical water; Koi requires cold water. These environments are incompatible.