Can swordtails live with black neon tetras?

Verdict
Yes

Yes. Swordtails and black neon tetras get along in the same tank. Both are fine at 73–79°F. Plan on at least 30 gal.

SwordtailSwordtail72–79°F · pH 7–8.3 Black neon tetraBlack neon tetra73–81°F · pH 5.5–7.5

Why it works

Water side by side

55°60°65°70°75°80°85°90°Both: 73–79°Swordtail 72–79°Black neon tetra 73–81°
The green band is the temperature range both can live in.
456789Both: 7–7.5Swordtail 7–8.3Black neon tetra 5.5–7.5
The green band is the pH both tolerate.

Size to scale

Swordtail · 5 inBlack neon tetra · 1.5 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

SwordtailBlack neon tetra
Temperature72–79 °F73–81 °F
pH7–8.35.5–7.5
Adult size5.0 in1.5 in
Minimum tank30 gal15 gal
TemperamentSemi-aggressivePeaceful
Swims atMiddleMiddle
GroupGroups of 3+Groups of 6+
DietOmnivoreOmnivore

Better tank mates for swordtails

All swordtail tank mates

Better tank mates for black neon tetras

All black neon tetra tank mates

Questions

Can swordtails live with black neon tetras?

Yes. Swordtails and black neon tetras get along in the same tank. Both are fine at 73–79°F. Plan on at least 30 gal.

What temperature suits both swordtails and black neon tetras?

73–79 °F. Swordtails need 72–79 °F, black neon tetras need 73–81 °F.

What size tank do swordtails and black neon tetras need together?

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