Poor pairing in a typical community
Their preferred temperature ranges and husbandry styles do not align well long term.
Practical response: Use a cool-water goldfish community or a tropical community rather than forcing a compromise temperature.
Molly
- Adult size
- 9 cm / 3.5 in
- Tank reference
- 90+ L / 23.8+ US gal
- Group
- 4+
- Zone
- mid
- Temperature
- 24–28°C / 75.2–82.4°F
Fancy Goldfish
- Adult size
- 20 cm / 7.9 in
- Tank reference
- 150+ L / 39.6+ US gal
- Group
- 2+
- Zone
- mid
- Temperature
- 18–24°C / 64.4–75.2°F
Water parameter overlap
Behavior and space
A comparatively large, high-output livebearer needing space, hard water and robust filtration. Heavy-waste cool-water fish; fancy varieties need generous volume and strong filtration.
A compatibility answer should also consider the actual tank dimensions, number of each fish, filtration, planting and other occupants. Two species can be reasonable together in a long, structured aquarium yet become a poor pairing when compressed into a small footprint.
Common questions
Can Molly live with Fancy Goldfish?
The StockingLab verdict is avoid: Their preferred temperature ranges and husbandry styles do not align well long term.
Do their temperatures overlap?
24–24°C / 75.2–75.2°F shared range.
Should I trust compatibility calculators completely?
No. Individual behavior, sex ratios, breeding condition, aquascape and tank size can change the outcome. Use the result to identify risks, then verify care requirements before purchase.