Cardinal Tetra and Molly: Can They Live Together?
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Side-by-side comparison
| Factor | Cardinal Tetra | Molly | Assessment |
|---|---|---|---|
| Water temperature | 73–81°F | 72–82°F | Overlap 73–81°F |
| pH | 5.5–7 | 7.5–8.5 | No overlap |
| Hardness | 1–8 dGH | 15–30 dGH | No overlap |
| Adult size | 2.0″ | 4.0″ | 2.0× difference |
| Temperament | Peaceful | Peaceful | Both peaceful |
| Swim level | Mid | All | Different zones |
| Minimum tank | 20 gal | 20 gal | Together: 32 gal+ |
Shared water parameters
- Temperature both tolerate: 73–81°F
- No shared pH window.
- No shared hardness window.
- Recommended combined tank: 32 gallons or larger
Risks and things to watch
Incompatible pH
These species want genuinely different water chemistry. Adjusting pH with chemicals introduces swings that are more harmful than the mismatch itself.
Group requirements
Compatibility is not only about the two species getting along — each still needs its own social setup met inside the same tank.
- Cardinal Tetra — minimum group of 6. Budget tank space for the whole shoal, not one fish.
- Molly — minimum group of 3. Budget tank space for the whole shoal, not one fish.
Frequently asked questions
Can cardinal tetra and molly live together?
Possible, with conditions. Cardinal Tetra and Molly can work, but this is a conditional yes rather than easy one. Read the risk section below before buying — the pairing usually fails for one specific reason, not because of general incompatibility. Plan on 32 gallons minimum.
What size tank do cardinal tetra and molly need together?
Plan for at least 32 gallons. Cardinal Tetra alone needs 20 gallons and Molly needs 20, but combined stocking needs headroom for filtration and swimming space, not just volume.
What temperature suits both species?
Both are comfortable between 73 and 81°F. Set the heater to the middle of that window and keep it stable.
What pH works for both?
Their pH requirements do not overlap (5.5–7 vs 7.5–8.5).
Will molly eat cardinal tetra?
Unlikely. At 4.0″ versus 2.0″ the size gap is not large enough for predation, though fry and juveniles are never safe in a community tank.
How should the tank be arranged?
Use plants, wood and rock to break sight lines, keep open swimming space along the front, and add the more territorial species last so it cannot claim the whole tank before the other settles in.
Explore further
Assessment generated from our compatibility methodology: parameter overlap, adult size ratio, temperament and swimming zone. Reviewed by Marcus Rivera.