OK bit of an update... The tetra that looked the worst has now died, and I now have transferred four of the tetras to a hospital tank... there is now one with bent spine too.
Now my understanding of the glo light tetras is the males are smaller and skinnier, whereas the females a more rotund... all the "sick" fish thus far seem to be females... the males are fine, as are all the other fish in the tank (corys, rams, ottos etc)... so am I missing something? Maybe they egg bound?
Some images of the ones in hospital:
http://www.iforce.co.nz/View.aspx?i=s1d4b42w.jpg - Notice the flared gills on the one at bottom of photo.
http://www.iforce.co.nz/View.aspx?i=ecexggkb.jpg
http://www.iforce.co.nz/View.aspx?i=3dvdr3qr.jpg
http://www.iforce.co.nz/View.aspx?i=wi42xcrt.jpg
http://www.iforce.co.nz/View.aspx?i=q2rfb0oh.jpg
So, I'm really starting to get confused, water parameters (ammonia, nitrates, nitrites) are all fine... The afflicted fish still seem to be breathing heavier than the others, even though I have turned up the air pump and pointed the spray bar on the filter up and caused even more surface agitation...
Maybe I am overfeeding them? I have given peas in recent days which they have had a go at and eaten... or maybe there isn't anything wrong at all???
Help...confused
On a positive note, I now have a little hospital tank so I can isolated sick fish faster in future.