Neon Tetra Is Sick. Please Help.

[ilwayne]

Tank size: 30 gallons (US)
pH: 8.4
ammonia: 0.00
nitrite: 0.00
nitrate: 40
kH: 300
gH: 300
tank temp: 78

Fish Symptoms (include full description including lesion, color, location, fish behavior): neon tetra in the tank has turned black along the head and top of body. Fins are ragged, tail fin is nearly a stump. No noticable red delineation as in fin rot that I've seen before. Fish is barely swimming (I've mistaken it for dead several times over the past 12 hours) and hiding behind a cave, almost burrowing into the gravel. It's eating a little, but not much (one bite of food about the size of a large sand grain).

Volume and Frequency of water changes: weekly 25% water changes

Chemical Additives or Media in your tank: no chemical additives except Tetra Aqua-safe during water changes. Tank has charcoal filter (currently two months old, gently rinsed in used aquarium water during water changes if it looks a little gunky) in a mechanical filter and undergrav filter powered by power head.

Tank inhabitants: two female black mollies, one serapae tetra, one neon tetra (the sick one) *I know they are schooling fish but these are the last remains of an outbreak of something that caused cysts/pustules, erratic swimming, and eventually death and until I figure out what caused the outbreak, I'm reluctant to get more fish*

Recent additions to your tank (living or decoration): Nothing, living or otherwise, has been added to the tank in three months.

Exposure to chemicals: none that I'm aware of.

 

[SPLiSH]

Sorry, other than fin/body rot nothing springs to mind...

I recommend that you isolate the fish in a hospital tank if you have one, keep it's water clean and warm.

I really am sorry that I cannot be of more use.

 

[WILDER]

Black pathces can be ammonia burns that are healing.
It sounds like a parasite infestation to me any laboured breathing or flicking and rubbing against objects.
Is the red stripe still vibrant.
Also check on the neons if they have lumps that go to a point in the tummy area.
Took another looks don't like the sound of the cyst i beginning to wonder if its ntd.

Take a look here to rule it out.
http/freshaquarium.about.com/cs/disease/p/neondisease.htm

 

[ilwayne]

Well the fish is dead, but I still am very interested to know what caused it. Not much of an "emergency" anymore, though.

The black coloration wasn't patches and wasn't even external...it was almost as if my neon tetra suddenly became a black neon. The entire "silver" portion of the body was darkly pigmented. Wish I'd gotten a picture before he died. The red and blue stripes were still quite vivid.

The cysts were on other fish that died prior to this one. This neon didn't have any cysts. And yeah, I had about come to the conclusion that I had an outbreak of NTD in the tank at the time. The only odd thing about it was the fact that the fish didn't all die in a short period of time. One or two would begin showing the cysts and other classic NTD symptoms. I would isolate and observe and occasionally euthanize before they got too bad. Then things would be fine for weeks or occasionally months, then BAM another few fish would show up with the cysts. No new fish had been added during the interim, either. We lost a total of 22 fish over a span of eleven months to NTD or swim bladder disease (different set of symptoms in the fish I consider to have died of swim bladder, obviously), all having come from the same store. I'm quite frustrated and think from now on I'll be ordering my fish online.

Just to avoid future issues, I'd love some feedback on anything you may have spotted in my OP that I might be doing wrong. Is my water quality ok? Water changes? I hate having my fish die on me, especially in what certainly seems a quite painful way and if there's anything I can do to prevent it, I'm open to it.

 

[WILDER]

On black widow tetras heard the black patches can be cancer, so that all i can think of really.

Look under black patches it mentions something about ntd.

http/www.fbas.co.uk/ASK3.html#widows