Compatibility Overview
Guppy 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 | Guppy | Koi | Verdict |
|---|---|---|---|
| Temperature | 72–82°F | 50–75°F | ⚠️ 72–75°F (narrow) |
| pH Range | 6.8–8.5 | 7.0–8.5 | ✅ 7.0–8.5 |
| Temperament | peaceful | peaceful | ✅ Compatible |
| Adult Size | 2.5 in | 24 in | ❌ 10× difference |
| Min. Group | 3+ | 2+ | See below |
| Min. Tank Size | 100 gallons (for both species) | — | |
✅ Compatibility Positives
❌ Incompatibility Reasons
Species Profiles
Guppy — Poecilia reticulata
Hardy and colourful livebearers. Males' long flowing tails make them targets for fin-nipping species. Very prolific breeders.
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 Guppy live with Koi?
Generally not recommended. Guppy 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 Guppy and Koi together?
A minimum of 100 gallons is recommended for keeping Guppy and Koi together. A larger tank improves water stability and reduces territorial conflict.
What temperature suits both Guppy and Koi?
72–75°F (narrow)
Is a Guppy aggressive toward a Koi?
Guppy is peaceful and Koi is peaceful. Guppy requires tropical water; Koi requires cold water. These environments are incompatible.