I mean is there any difference species-wise and care-wise.
Yes to both questions. These are two distinct species from very different habitat types.
There are actually three described species [
Paracheirodon innesi, P. axelrodi and
P. simulans] of the "neon" appearance, and one newly discovered species that will not be seen by hobbyists for quite a while given the very remote area in which Heiko Bleher found it in 2006. The three described species are obviously related, and phylogenetic analysis confirms this; they are in the genus
Paracheirodon, where the fourth species will undoubtedly be classified when it is eventually described.
Paracheirodon innesi, the original "Neon" Tetra, occurs in habitats having cooler water in blackwater or clearwater streams of the upper Amazon basin in Peru, sections of the Rio Ucayali, and elsewhere. Most commercially available fish are tank raised, but they retain their needs/requirements.
P. axelrodi, the cardinal tetra, occurs in the Amazon Basin, primarily the northern tributaries of the Rio Negro in Brazil and Peru [Brazilian form], and the Orinoco basin in Columbia and Venezuela [Columbian form]. Occurs in forest streams and creeks in slow or standing water, well shaded by vegetation and frequently having aquatic plants. This species can live in warmer water than the neon tetra.
None of these species occur in brightly-lit areas, so floating plants are advisable to shade the tank. The cardinal actually has been described as having a light phobia. Soft acidic water is preferred.