Symptoms
This disease was originally described in Neon Tetras, but can affect many other species of fish. In Neons, one of the early signs of this disease is a loss of the red colour, and difficulty swimming Note that there is a so-called "false neon disease", which is bacterial, and shows very similar symptoms. It is impossible for the home aquarist to determine for certain the difference between NTD and false NTD on the basis of visible symptoms alone, without laboratory backup. This disease has also been confused with Columnaris.
Causes
The disease is caused by a microsporidian parasite. The disease is most likely to be passed on from newly acquired fish, which have not been quarantined.
Possible cures
These parasites are very resistant to medications, and there are no proven effective treatments. Some anti-parasite medications claim to treat this disease, but there effectiveness is debatable. Some apparant 'cures' may have been the result of successful treatment of false-NTD. The best course of action is to isolate sick fish quickly, and maintain good water quality to reduce the chances of more fish succumbing to the disease. The use of a diatom filter, which can reduce the number of free parasites in the water, may help.
this is a pretty good link:
http://203.116.88.76/content/phase1/...tor_Other.html
BTW cardinal tetras dont seem to suffer from NTD and they look exactly the same except the red strip goes all the way along the body unlike the neon whos red stripe runs from the tail about a quarter along the body.
I had a case of NTD in my tank and it wiped out all my glowlight tetras and harlequins.......if you are unlucky and get an outbreak remove any dead or dying fish ASAP cos if your other fish eat them they eat the spores that carry NTD and then they get affected. if you get NTD and it seems like it is no longer present dont add any new fish for at least 6 months and when you do make sure there quarrentined.