Can Goldfish and Molly Live Together?
Short answer: No. Goldfish needs 50-74°F and Molly needs 72-82°F. Keep them in separate tanks, or pick one of the safer tank mates listed below.
Can Goldfish and Molly Live Together? No, not as a long-term shared setup. Goldfish stay healthiest in cool water while Mollies need steady tropical warmth and hard, alkaline conditions, so one species is always kept outside its range.
| Factor | Goldfish | Molly | Verdict |
|---|---|---|---|
| Temperature | 50–74°F | 72–82°F | ⚠️ 72–74°F (narrow) |
| pH Range | 6.5–8.0 | 7.5–8.5 | ⚠️ 7.5–8.0 (narrow) |
| Temperament | peaceful | peaceful | ✅ Compatible |
| Adult Size | 12 in | 4 in | ⚠️ 3.0× difference |
| Min. Group | 1+ | 3+ | See below |
| Min. Tank Size | 100 gallons (for both species) | — | |
Compatibility Positives
Incompatibility Reasons
Temperature and Habitat Requirements Conflict
Goldfish stay healthiest in cool water while Mollies need steady tropical warmth and hard, alkaline conditions, so one species is always kept outside its range.
A Safer Plan for Goldfish and Molly
Keep Mollies in a heated, hard-water tropical tank and give Goldfish a cool, heavily filtered setup of their own.
What Actually Goes Wrong
The temperature gap is the part that cannot be designed around. One side of this pair is a cool-water fish that does best between 65 and 72 °F; the other is a tropical livebearer that wants 75 to 82 °F. Setting a heater to a compromise near 74 °F leaves both animals mildly stressed rather than either one comfortable — the cool-water fish runs a faster metabolism than it should, while the livebearer sits at the bottom of its range, where it becomes noticeably more prone to fungal and bacterial infection.
Hardness pulls in the same direction. Livebearers do best in mineral-rich water above pH 7.5, which the other fish tolerates but does not need. The problem is holding that chemistry steady: a heavy waste producer in the small, warm tank the livebearer prefers will swing pH and nitrate faster than a weekly change can correct.
A size and feeding mismatch then shows up later. A mature specimen reaches six inches or more in the body and will sample anything that fits in its mouth, starting with fry and eventually including an adult livebearer that swims too slowly to get out of the way. The pairing often looks fine for a first year, while both fish are still small, and fails as the larger one grows.
If the goal is one tank rather than two, choose the temperature bracket first and stock around it. A cool-water setup works with white cloud mountain minnows or hillstream loaches; a heated, hard-water setup works with platies and swordtails.
Species Profiles
Goldfish — Carassius auratus
Classic pond and aquarium fish that prefer cool water. Heavy waste producers that require robust filtration. Will eat small fish and shrimp.
Molly — Poecilia sphenops
Hardy livebearers that prefer alkaline, hard water — sometimes slightly brackish. Prolific breeders; peaceful community fish.
Frequently Asked Questions
Can Goldfish live with Molly?
No. Their temperature ranges do not overlap safely, so one of the two would spend its life outside its healthy range.
What is the biggest risk for Goldfish and Molly?
Goldfish stay healthiest in cool water while Mollies need steady tropical warmth and hard, alkaline conditions, so one species is always kept outside its range.
Would a larger tank make Goldfish and Molly compatible?
More space can reduce some conflict, but it cannot solve incompatible water type, temperature, predation, or core welfare needs.
What is a safer alternative to keeping Goldfish and Molly together?
Keep Mollies in a heated, hard-water tropical tank and give Goldfish a cool, heavily filtered setup of their own.
Safer Tank Mates for Goldfish and Molly
The highest-scoring compatible partners for each species in our compatibility data.
For Goldfish
- Weather Loach — 98/100
- Bristlenose Pleco — 87/100
- Denison Barb — 87/100
- Koi — 86/100
- Swordtail — 79/100
For Molly
- Guppy — 96/100
- Platy — 92/100
- Swordtail — 89/100
- Electric Yellow Cichlid — 88/100
- Peacock Cichlid — 87/100
Related Compatibility Guides
Tank size scenarios
Use the scenario that matches the actual group sizes and temperament you plan to keep.
| Scenario | Tank | When it applies |
|---|---|---|
| Minimum viable | 100 gal | Only for the recommended minimum groups, mature filtration, and close monitoring. |
| Recommended community | 150 gal | Adds territory, swimming room, and a safer buffer for behavior. |
| Low-conflict setup | 180 gal | Best when keeping larger schools or reducing territorial pressure. |