Urgent: Neon not looking too hot

[fishscale]

One of my neons is not looking good. His belly is sunken, he seems listless, it looks like he is losing scales or something (patchy coloration). He probably won't make it, but I want to make sure this isn't something that will spread to the other fish. Background info:

Tank Size: 10 gallon
Filter: Penguin 110 w/ Biowheel removed
Water Parameters:
Ammonia: 0
Nitrite: 0
Nitrate: 15 ppm
pH: 7.3
No dosing currently
Time set up: 7 months

Inhabitants: 4 Neons, 9 Diamond Tetras (4 adults, 2 surviving juvies from the last spawn, 3 fry), 1 oto (on loan from shrimp tank), RCS, Amanos

Plants: HM, some kind of crypt, unid'd bulb that somehow sprang up (must have come in with other plants).

I have not introduced any new fish to this tank for 4 months.

All other fish are healthy and eating well, full bellies.

I believe this is some kind of parasite or disease. The fish looks like it is being eaten away (looks like scales are falling off or something).

I have inverts and plants, so I need to be careful with what I treat with. Any recommendations/diagnosis?

[eon17]

if you have not introduced anything then its doubtfully paracites. The most important thing is to put him in his own tank as to not affect others or if you need to euthenize him.

[mistergreen]

I just bought a rasbora with the same symptons.. It could be columnaris.

[fishscale]

I euthanized him, just have to hope he didn't infect the rest of the tank. Symptoms resembled neon tetra disease, which, apparently can spread to more than neons.

[fishscale]

Still concerned, anyone have any more info? I looked at pictures of Ich, velvet, columnaris, and septicemia, and it didn't resemble any of them.

[fishscale]

Here's what I can tell you: the colors were actually still fairly bright, the fish did not fade or become pale. However, the red area of the neon was darker than usual, his belly appeared shrunken, and there was a chip of white on the blue stripe. This did not resemble ich, as it was much larger than what ich should look like. It looked as though another fish had taken a nip out of his stripe and pulled out some scales. I raised the temp and did several water changes, but there was no change. The fish would swim to the bottom of the tank, then float slowly upwards, and swim down again. I'm paranoid now, and every time I use something in that tank, I put it through a dilute bleach dip.