Help! Very ill neon tetra

[calebs787]

A little background first. These guys are kept in a school of 5 now. There was 8, 1 was eaten, 2 mysteriously dissapeared. The tank specs are:
Ph:7.8
Ammonia: 0ppm
Nitrite: 0ppm
Nitrate: 80ppm
Temp: 80.5°F
55 gallon tank kept stocked with: 5 neon tetra, 1 neon purple tetra, 3 zebra danios, 1 rainbow fish, 3 red wag platys, 2 tiger barbs

All other fish in the tank appear to be fine. No fin damage, no odd behavior. But this one for some reason has most of its caudal fin gone and is gasping very heavily. Also considerable smaller than the other 4 like him. I've removed him from the tank into a 5 gallons until I figure out what's going on. I just need to know what's wrong and if its treatable and if so how to treat it.

 

[Barry Tetra]

Your nitrate is too high, do 80% daily water change substrate clean, make sure water is free of chlorine and chloramine before adding to the tank.

 

[Colin_T]

Does the fish have white bits sticking out of its face and tail or is that the photograph?

Can you post a couple more pictures showing both sides of the fish?
Make sure they are in focus.

-----------------
As mentioned by Barry, your nitrates are pretty high. You want to keep the nitrates as close to 0 as possible, and definitely under 20ppm.

The easiest way to reduce the nitrates is by doing a 75-80% water change and gravel cleaning the substrate every day for a week.
Make sure any new water is free of chlorine/ chloramine before it's added to the tank.

 

[JuiceBox52]

It looks like it is not just the photo @Colin_T

@Byron
Nitrate is too high.
What is your GH? Your platies need hard water, others need soft.
Barbs should be in a group of no less than 8 they will almost always show aggressive behavior if less than that.
Your zebra danios should be in a group of at least 5-6
Good luck