What I've heard from more experienced fishkeepers than myself- Don't bother with neons, they have been overbred and weakened and that's why so many are dying. Try seeing if you can get wild caught neons or even better ,cardinal tetras(looks like a neon but bigger and fuller reds and blues) are even more vibrant. Cardinals are wild caught and they are great fish but they really appreciate the softer water, they may cost you more, but you get what you pay for.
Try researching them and see if you would be willing to try them.