Hemigrammus bleheri or rummy-nose tetra.
In the tank there are now 5 fish. Actually that's not enough, but the emphasis in the tank is put on the cardinal tetras.
There are three species referred to as rummy-nose tetras:

- Hemigrammus rhodostomus (up)
- Hemigrammus bleheri (middle)
- Petitella georgia (down)

They look almost the same, though there are some small differences. The best scheme to differentiate the three species involves three features: the lower caudal peduncle mark, the extent of red, and the mid-body line leading into the center caudal bands.

Hemigrammus bleheri

Characidae, Tetragonopterinae

Habitat: South America (Brazil)
Length: up to 2,0 inch (5 cm)
Temperature: 75-79 °F (24-26 °C)
pH: 6
DH: 2-7°