The Black neon is a fun group of about 4 cm for tanks from about 60 cm. Although they do need each other's company in the aquarium they will not really swim together when they are at ease. If they are less at ease because of the presence of much larger fish, a good group of 20 to 30 pieces is a spectacular sight.
The original location of this fish is South America but nowadays almost exclusively offered as captive bred. Provided they are kept in a group they will show their beautiful colors in aquariums with limited lighting or dense vegetation (hiding places). Some air flow is also good. As companion you can take many other small peaceful fish like various dwarf cichlids (Apistogramma) or angelfish.
When the pH is not too high (6.5-7.0) and the temperature at about 25 degrees Celsius they will keep without difficulty. You can feed them both dry, frozen as small live food.