Black Neon Tetra Refusing To School

[Nick-Alan]

I have the following schooling fish:
5 neon tetras
5 black neon tetras

They form three schools.
1 group of 5 neon tetras
with
1 group of 5 black neon tetras
OR
1 group of 10 neon tetras.
(only when the gouramies swim near)


Recently, one neon black tetra has not been joining the usual schools. he just swims in a corner behind a rock. It looks really sad, especially since his friends are playing around having all the fun.

Is this normal?

Can I help him be with his friends?

Could he hate his friends?

 

[Rainy day]

I've noticed sick tetras refuse to school, does he show any other symptoms? Either that or he's just stressed and doesn't want to be in the open, even if he'll feel more secure with the school.

 

[JoeCamaro]

I agree with @Rainy day. He coukd be sick, they do that when sick.
Or maybe it is just a rebel tetra, but I would guess sick.
Have you noticed any change in feeding also?