Help! Sick Fish

I have a neon tetra out of 6 that has lost color in its tail and seams to have some atrophy. Its still swimming and schooling, its eating ok, it just has lost that distictive blue and red stripe towards the tail and the tail seams to be paralized in a position to the right of midline.

Background - I live in Tempe, Az (hard water) the fish resides in a ten gallon tank with 11 otherr tetras, and pleco, and half a dozen ghost shrimp. Yes, I know, a little over crowded. There are also 5 live plants in the tank. I was unaware of the nitrate level as this test does not usually come with a simple master kit and when I took some water to the pet store, the said I was way to high, upwards of a 180/ppm. I have since corrected with 25% water changes every other day and after buying a test kit, I am now down to less than 5/ppm. The resident expert at the facility I went to said that it looks like my neon has a bacterial infection so after correcting the water, I started the tank on eurythromyicin. There has been no improvement with this one fish and no other fish seem to be infected. Does any one have any ideas? Could it just be an injury, maybe got stuck by the pleco?

Water as of this AM:
ph 6.6
water temp 79
specific gravity of 1.000
NO2 <0.05
NH4+ < 0.25
Nitrate <5/ppm

Running an Aqua clear 30 filter, air pump, homemade CO2 generator with ladder type diffuser and the light is on ten hours a day.

Thanks for any help!

John

Antibiotics wipe the benefical bacteria out in the filter.
Bad water quality can make fish go pale.
Or it could be ntd.
Water changes and increase aeration.
It might be best to put him out of his misery. If he's paralized.

Signs of ntd are.
Red area will look bleached out. Or a milky substance on red stripe area.
Blue area can turn a golden yellow colour.
Fish will become restless and leave shoal
Fish will swim around in a odd manor.
Fish will sometimes have a black lining around the red area.
Bent spine.
Finrot.
Later stages dropsy and popeye.

I took the carbon filter out and just left the sponge and the other media in the filter. The guy told me that much. I just have a hard time with the ntd. It fits but it doesn't. I hope this photo uploads so you can see.

Can you enlarge the pic as can't see a thing.

Sorry, new to the whole pic thing

The white does it look fluffy on the tail or just bleached out.
Any black linning around the red tail area.
Does his blue area look yellowish,
Is his spine bending.

His spine is bent now at a 90 degree angle. The color is bleached out and now there is a faint black line across his ventral side only in the infected area. there is no yellowing. What ever this is seams to be getting worse. Its taking over more of his body but he's a scrapper. He continues to dart around and eat even though his tail is at a 90 degree angle.

I would put him out of his misery as he puts the rest of the fish at risk.
Just hope its not ntd or fish tb,