Can pencilfish live with black neon tetras?

Verdict
Yes

Yes. Pencilfish and black neon tetras make a good pair. Both are fine at 75–81°F. Plan on at least 15 gal.

PencilfishPencilfish75–82°F · pH 5–7.5 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: 75–81°Pencilfish 75–82°Black neon tetra 73–81°
The green band is the temperature range both can live in.
456789Both: 5.5–7.5Pencilfish 5–7.5Black neon tetra 5.5–7.5
The green band is the pH both tolerate.

Size to scale

Pencilfish · 2 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

PencilfishBlack neon tetra
Temperature75–82 °F73–81 °F
pH5–7.55.5–7.5
Adult size2.0 in1.5 in
Minimum tank15 gal15 gal
TemperamentPeacefulPeaceful
Swims atMiddleMiddle
GroupGroups of 6+Groups of 6+
DietOmnivoreOmnivore

Better tank mates for pencilfish

All pencilfish tank mates

Better tank mates for black neon tetras

All black neon tetra tank mates

Questions

Can pencilfish live with black neon tetras?

Yes. Pencilfish and black neon tetras make a good pair. Both are fine at 75–81°F. Plan on at least 15 gal.

What temperature suits both pencilfish and black neon tetras?

75–81 °F. Pencilfish need 75–82 °F, black neon tetras need 73–81 °F.

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

At least 15 gal, set by the pencilfish. Add space for each extra fish.