what sized tank?
is it cycled?
what fish are already in the tank (if any)?
is it planted?
what are you water perameters? (ammona, nitrates, nitrites, pH)
Neon and Cardinal Tetras look exactly the same only the Cardinal Tetras have more color. To better help you out with your question we need to know how big your tank is.
I couldn't keep NT's alive, but... I got 6 Tin foil Tetras, and they have thrived to the point that a few of them are as big as my hand. It's crazy! Their appetites are voracious. A friend came over and said, "I like your Angel fish".
I didn't bother to tell her they were tetras, I didn't figure she'd believe me anyway. :look: