Tetra spiral dance of death

One of my Head & Tail lights is doing something like this; I noticed it last night. He can put on spurts of activity and he did eat this morning, but when he's still, he has some troubles with orientation. No upside-down swimming (as of this morning before I left for work), but he tended to drift into a vertical, head-up position. He shimmies/shakes at times as well.

The other fish are fine, so I kind of doubt he has something that's catching.

Water tested this morning showed ammonia 0, nitrites as close to 0 as the test gets (Tetra tests). The temperature around 78 degrees.

As the troubled fish was always grumpy, I think they others (3 more H&T and two black tetras) are getting some revenge on him by pushing and chasing him around (he is able to get away and find a quiet place). I don't think they'll miss him if/when he passes on. If he doesn't improve, I may just pass him along myself. This would be sad, as he and two other H&Ts helped me cycle the tank in August (my first aquarium since the 1960s), but his grumpy, "this is *my* territory!" attitude has not exactly endeared him to me.

I hope to add a ten-gallon or maybe larger tank this weekend (I've arranged a ride to my LFS). The current Eclipse 6 has taught me a lot of valuable lessons. The cycling went well (I did lose an H&T at 60 hours [couldn't swim upright], but the others did fine), and other than the current troubled fish, I'm happy and want to branch out a bit. Probably more black tetras and maybe some bloodfins. I'm not into more expensive, flashy fish, I just want to watch happy fish.

Stats:
6 gallon Eclipse System 6
Anarchis, Watersprite(?), green temple plants (which may need more light)
some snails
6 (maybe soon 5?) fish
gravel substrate, rocks: jasper, polished petrified wood, some crystals
City: Albuquerque
LFS: Clark's Pet Emporium

Just in case ya'll didn't know, and this is kind of interesting in this case, red-eye tetras and head-and-tail light tetras are the same. I had six; one died early on, and I think two have been recently eaten by my ghost knife--he's grown big enough!!!

could it be neon tetra disease? http://freshaquarium.about.com/cs/disease/p/neondisease.htm

It's not specific to tetras, but was named that because it was first diagnosed in neon tetras. The disease organism is Pleistophora hyphessobryconis. Unfortunately, it seems extremely resistant to medications, and almost always leads to a slow agonizing death for affected fish

Either that or possibly Whirling Disease? http://www.cichlid-forum.com/articles/diseases_int_protozoan.php

"this is kind of interesting in this case, red-eye tetras and head-and-tail light tetras are the same", that's news to me, thanks! I notice my black neons have that irridescent red upper, um, eyelid, too. As for neon tetra disease, I googled "tetra disease" and they all described the same thing, which didn't describe what was happening to my single H&T. "Whirling Disease"? I hadn't thought of that... I think it may be related to Jacob-Croitzfeld (sp?) as it happens in the wild to, oh, trout; the disease is aka "mad cow". My sick H&T was still hanging on when I got home Friday evening, but he looked so bad, not even noticing the food I put in the tank (the other 5 sure did notice, it was feeding time anyhow), and he so was skinny and boney looking and scoliotic looking, that all I could think was "this fish isn't getting any better..." so I netted him (not easy, he gave me a run... swim for my money... if only he had shown *some* interest in the food... ) and he became compost (which I think is more useful than flushing 'em). Here it is almost 24 hours later and the other fish are still fine. I continue to look forward to acquiring a 10 gallon (or more?) tank on Sunday