Neon Tetras are dying

[JamesTasker]

When I got home this evening, one of my 8 neon tetras and a platy fry were dead. The symptoms for the tetra are slight loss of red colouration, damaged fins, and heavy breathing (I know fish don't breathe but that's how i would describe it). It looks like the symptoms have started on the others and I don't know how to save them even if I can. I added some five banded barbs on Saturday so this could be the problem. I read that they weren't aggressive and I haven't seen any agressiveness either but maybe they only do it when I'm not around (this could account for the damaged fins?)? I did a water change on Sunday and the water is fine - I know my tank is overstocked by the inch/gallon rule but its not if you calculate by surface area. However, my ancistrus has been taking breaths at the surface so maybe the oxygen content is too low? I don't have an airstone but I have just turned on the airflow on my internal filter. Thank you very much for any help you can give me.

 

[Tempestuousfury]

The fast breathing and surface breathing means lack of O2. the best remedy is to do water changes, lower the number of fish (if possible), create water surface disturbance, and slightly lower the temp if it's too high.

As for the loss of coloration, it might be that the tetras are sick, but it could also be neon tetra disease (there are a bunch of posts about this disease).

As for the barbs, they are said to be aggressive, though I'm not sure about the type you have. Have you noticed ripped fins or the like?