tetras missing an eye

Question
QUESTION: I've recently upgraded my community tank to a larger setup, I set everything up and let the water cure with a anti-chlor , and a bacteria booster for about 2 days. I moved my current fish over after the 2nd day, and they all seemed to be fine, so two days later i purchased five neon tetras from m y local petsmart and have had very poor luck. Of the first five i bought, they all looked fine initially (one female was about to scatter eggs), but after about two days in the new tank, one of them came up missing an eye and then died. I used an anti-parasite medication. Since the first one dying, i've had 4 other go, and then i just came home for my lunch break, and 3 more (of the replacements) are missing an eye. I have them with a pair of swordtails, a single guppy (her mate and sisters died several months ago in the previous tank) a cory catfish, and a rubber lipped plecostamus.
The filter is one from wal-mart (aqua-tech), it has the 2 part filter cartridge, and the bio-fiber.
My local ph is high (in the 8 range), but i've managed to bring it down (over the past week to about 7.5), which is the same as the pet store i've purchased fish from. Ammonia doesn't register on  my ammonia test kit, nitrites are below 20ppm. Haven't done a water change yet.
Only otehr thing of interest is a piece of african knotted drift wood that is in there. i've never used it before, unsure if it may be causing the problem...
Thank y ou for your time!

ANSWER: Hi Tommie;

A disease really can't cause the loss of eyes like that. I would suspect you have an aggressive fish that is biting your neons. Plecostamus can do that very easily, especially at night as your fish rest near the bottom of the tank in the dark. The swords or the lone guppy could even be responsible. There can definitely be an unusually aggressive individual of any of those. Or, the neons are simply weak from the elevated nitrites and getting picked at by any of the others. Watch them from a distance for awhile so they are acting normally (not reacting to your presence) and see what happens.

At Your Service;
Chris Robbins

---------- FOLLOW-UP ----------

QUESTION: yea i gave you the nitrate reading.. the nitrites are below 0.5 ppm.
and it appears to be some sort of mouth fungus, I noticed it on the two remaining ones today, and moved them to my quarantine tank. However, i've treated them with a fungus medication before, but it hasn't worked. any suggestions?

Answer
Hi Tommie;

It may be a bacterial infection called Columnaris. It looks very much like fungus but is treated with antibiotics instead of antifungals. Tetracycline is usually the most effective for this particular disease. It is available under many brand names at fish stores.

Make a daily 25% water change in the quarantine tank to keep their immunity strong too. Also add aquarium salt. Columnaris hates salt and it also strengthens your fish. Your fish can tolerate 1/2 teaspoon of salt per gallon. Add more every time you change water but only for the replaced water. In other words, if you replace two gallons of water, add back 1 teaspoon of salt.

You can also add a product called "Melafix". It helps soothe the raw areas and aid in regeneration of damaged tissues. It can't cure an established infection but it certainly can help the antibiotics work.

Here is a web page about columnaris;

http://freshaquarium.about.com/cs/disease/p/columnaris.htm

Good luck....

At Your Service;
Chris Robbins