Can fancy goldfish live with dwarf neon rainbowfish?

Verdict
No

No. Fancy goldfish and dwarf neon rainbowfish should not share a tank. Fancy goldfish are coldwater animals (65–74°F); dwarf neon rainbowfish need 75–82°F. No temperature suits both.

Fancy goldfishFancy goldfish65–74°F · pH 7–8 Dwarf neon rainbowfishDwarf neon rainbowfish75–82°F · pH 6.5–7.5

What to watch

What works

Water side by side

55°60°65°70°75°80°85°90°Fancy goldfish 65–74°Dwarf neon rainbowfish 75–82°
The ranges do not meet, so one of them would always be too warm or too cold.
456789Both: 7–7.5Fancy goldfish 7–8Dwarf neon rainbowfish 6.5–7.5
The green band is the pH both tolerate.

Size to scale

Fancy goldfish · 6 inDwarf neon rainbowfish · 2.5 in0"1"2"3"4"5"6"
Adult length in an aquarium. A fish can swallow anything that fits in its mouth, roughly a third to half its own length for predators.

Care at a glance

Fancy goldfishDwarf neon rainbowfish
Temperature65–74 °F75–82 °F
pH7–86.5–7.5
Adult size6.0 in2.5 in
Minimum tank30 gal20 gal
TemperamentPeacefulPeaceful
Swims atAll levelsMiddle
GroupAlone or in pairsGroups of 6+
DietOmnivoreOmnivore

Better tank mates for fancy goldfish

All fancy goldfish tank mates

Better tank mates for dwarf neon rainbowfish

All dwarf neon rainbowfish tank mates

Questions

Can fancy goldfish live with dwarf neon rainbowfish?

No. Fancy goldfish and dwarf neon rainbowfish should not share a tank. Fancy goldfish are coldwater animals (65–74°F); dwarf neon rainbowfish need 75–82°F. No temperature suits both.

What temperature suits both fancy goldfish and dwarf neon rainbowfish?

None. Fancy goldfish need 65–74 °F and dwarf neon rainbowfish need 75–82 °F, so the ranges do not meet.

What size tank do fancy goldfish and dwarf neon rainbowfish need together?

At least 30 gal, set by the fancy goldfish. Add space for each extra fish.