Neon Tetra Problem

[Hsieyun]

I have nine neon tetras in a 5 gallon tank, and they're swimming irregularly. They will start swimming downwards, and sort of do a sommersault in then act fine again. They have been bullied by my female betta. Is this normal?

 

[NEON98101]

Are they all 9 of them do that? Irregular swimming or sommersault. I need you to explain what is the sort of sommersault neon do. Anyway, is 1 of them do or 2 of them do side by side?
How many of the 9 do irregular swimming anyway? Are there any of the color washed out and whitish? Are any of the fish have dwarfed tail? Are there any visible injury?
I need more information. Beside the question above. Water condition(ph,temperature, dh or kh) also tank condition(like how long it has been set up, how often you do water change and how much, what kind of filter, heater etc).
However, I do believe female Betta to be harmless.
I just need more info and better explaination of sommersault and number of fish show the irregular swimming pattern. Otherwise, it's tough to determine the cause.
It could be lack of oxygen, some diesease like neon tetra diesease or could be breeding.

 

[Lateral Line]

If you have 9 Neons and a female betta in a 5 gallon, you are way overstocked. You will need to address that. Neons are sensitive to pollution, and in a tank that small, I can see a dozens ways for that to happen.