Molly and Pygmy Corydoras: Can They Live Together?
Side-by-side comparison
| Factor | Molly | Pygmy Corydoras | Assessment |
|---|---|---|---|
| Water temperature | 72–82°F | 72–79°F | Overlap 72–79°F |
| pH | 7.5–8.5 | 6.2–7.4 | No overlap |
| Hardness | 15–30 dGH | 2–12 dGH | No overlap |
| Adult size | 4.0″ | 1.0″ | 4.0× difference |
| Temperament | Peaceful | Peaceful | Both peaceful |
| Swim level | All | All | Same zone |
| Minimum tank | 20 gal | 10 gal | Together: 26 gal+ |
Shared water parameters
- Temperature both tolerate: 72–79°F
- No shared pH window.
- No shared hardness window.
- Recommended combined tank: 26 gallons or larger
Risks and things to watch
Size mismatch — predation risk
Molly reaches 4.0″ while Pygmy Corydoras tops out at 1.0″. As a rough rule, anything that fits in another fish's mouth eventually will. This is the main reason this pairing needs care.
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.
- Molly — minimum group of 3. Budget tank space for the whole shoal, not one fish.
- Pygmy Corydoras — minimum group of 8. Budget tank space for the whole shoal, not one fish.
Frequently asked questions
Can molly and pygmy corydoras live together?
Possible, with conditions. Molly and Pygmy Corydoras 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 26 gallons minimum.
What size tank do molly and pygmy corydoras need together?
Plan for at least 26 gallons. Molly alone needs 20 gallons and Pygmy Corydoras needs 10, but combined stocking needs headroom for filtration and swimming space, not just volume.
What temperature suits both species?
Both are comfortable between 72 and 79°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 (7.5–8.5 vs 6.2–7.4).
Will molly eat pygmy corydoras?
It is a real risk. The size difference is 4.0×, and anything that fits in a fish's mouth is eventually treated as food.
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.