Hello everyone, can somebody help me please....I am relly worried.

I have a twenty gallon tank, 6 months old.
I have 9 neon tetras. Only one of them looks like he went into a blender...is he going to die? or spread to others? he is in really bad shape...I have been watching carefully for bullying but no one seems to be bothering the Neon tetras. and he is the only one that looks bad.
I already treated my tank parasites and fungus but I do not see improvement. I did two weeks treatments of each fungus and parasites. Rest two weeks in between with carbon filter and proper water changes.

What happened to my neon tetra? I have not had fish loss since I set up my tank. He might be the first one. I have read that Neon Tetras are hard to keep...

Are you sure its a he and not a she? I suspect its a mature female fish who has over eaten. The mature females have a tendency for that behavior ( if she goes around asking the other fish 'do i look fat?' then you can be certained its a female ). Is the stomach bloated with scales in disarray when you look closely?

The solution is to separate her from the rest and not feed her for about 2 days and make sure she is pooping before you let her join her original tank mates. From experience, the 'greedy' female neons will usually be the ones laying eggs. My theory is that their 'greed' is due to maternal instinct ( i.e they need more nutrients because they want to have babies)
If you have to feed excess food because of the other fishes in the tank and dont want the neon to over-eat then you may have to seperate her for good.
Hope this helped.

ps: If you want to breed neons, I would recommend buying a few neons from different shops ( rather than all from 1 shop) so that they have a bigger DNA pool. If not they are inbreeding from the same stock and the offspring will end up sickly or dumb.

Thanks Franco!
I did not want to wait for my neon to get chubby and weird again so I decided to set them apart.

Thank you!