3 Neons Dead!

[-FighterFishh]

Today at around 10am two of my neon tetras were found dead by my mum, and another has disappeared.
She said that she looked at them both and could not see any outward signs of disease.
They were kept in a shoal of six, and they had all been in the tank for about a week now. All of them had their fins up and were eating.
The other 3 are fine, but two of them seem to be constantly fighting.
The water is fine and they haven't been being chased around or nipped at, from what I've seen.
Any ideas on what caused their deaths?
Thank you

 

[Caprichoso]

Having no outward sign of disease either means they had an internal issue or you had ammonia in your tank. You said that the water is fine, as in you tested it? The reason the other ones aren't getting along is because they need to be in a school of 5 or more.

 

[Skins]

Neons are now regarded as quite a delicate fish which don't do as well in a tank where the filter is less than 6 months mature.

Keith.