Can cardinal tetras live with pencilfish?

Verdict
Yes

Yes. Cardinal tetras and pencilfish make a good pair. Both are fine at 76–82°F. Plan on at least 20 gal.

Cardinal tetraCardinal tetra76–84°F · pH 4.6–7 PencilfishPencilfish75–82°F · pH 5–7.5

Why it works

Water side by side

55°60°65°70°75°80°85°90°Both: 76–82°Cardinal tetra 76–84°Pencilfish 75–82°
The green band is the temperature range both can live in.
456789Both: 5–7Cardinal tetra 4.6–7Pencilfish 5–7.5
The green band is the pH both tolerate.

Size to scale

Cardinal tetra · 2 inPencilfish · 2 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

Cardinal tetraPencilfish
Temperature76–84 °F75–82 °F
pH4.6–75–7.5
Adult size2.0 in2.0 in
Minimum tank20 gal15 gal
TemperamentPeacefulPeaceful
Swims atMiddleMiddle
GroupGroups of 6+Groups of 6+
DietOmnivoreOmnivore

Better tank mates for cardinal tetras

All cardinal tetra tank mates

Better tank mates for pencilfish

All pencilfish tank mates

Questions

Can cardinal tetras live with pencilfish?

Yes. Cardinal tetras and pencilfish make a good pair. Both are fine at 76–82°F. Plan on at least 20 gal.

What temperature suits both cardinal tetras and pencilfish?

76–82 °F. Cardinal tetras need 76–84 °F, pencilfish need 75–82 °F.

What size tank do cardinal tetras and pencilfish need together?

At least 20 gal, set by the cardinal tetra. Add space for each extra fish.