Neon Tetra Strange Behaviour

[Stephleona]

I have some platy's and 5 neon tetra's in my tank at present but recently one of them is behaving weird. It has separated from the group and chases them off when they come close? he seems to have also partnered up with one of my juvenile platy? is he just a bit confused? 
 
Any info welcome. Thank you

 

[PrairieSunflower]

Confident neons will separate and explore a bit more from the group.  Also, in lower numbers (bellow about 6-8) a bit more bickering between neons is common.  I upped my numbers beyond 10 (had 17 in total when I kept them) before the bickering died down.
 
What size tank do you have and how long has it been cycled?  Do you have plenty of plant cover for your fish to feel secure?

 

[Stephleona]

I just have a small tank 30 litre ish so didnt want to overcrowd it. Tank has been established for about a year it has got plenty of hiding spots for them to go. I have had the tetra's for 5 months or so but this one has just started showing this behavior. 

 

[PrairieSunflower]

That could be part of it, neons do prefer bigger (longer) tanks and swimming more distance.