Will 1 Neon Tetra School With Ember Tetra Or Dwarf Rasbora?

That's a silly pet shop policy. Just keep him while you try to locate a pet store or someone that will take it.

They wont behave the same with other species (especially smaller ones, and even more so with rasboras which are quite far apart).

Just don't keep him on his own in a 14L permanently, keep looking around and asking people.

Most people end up with only one or two of a species of tetras in their tank at some point, it's really not the end of the world and isnt an issue most of the time, but the tank size here would urge me to find it a new home.

There's a high chance the neon will start to bully any other fish, since it's not a in a group of its own kind in a bigger environment it's going to behave unnaturally/insecure.

 

where abouts are you peglegg i know if you were in the south west i'd come and collect the fellow to come live with my 13 neons

Dont give up on the 14 litre tank - Its a 3 g tank so that would be fine to keep a beeta in -- the recommended for bettas is 3 gallons as long as you have a heater filter and some plants

If not micro rasboras , or shrimp would also be good in there

Good luck let us know how you get on with rehoming the neon

 

Small fish are fine, but neons are pushing it too much. Since you haven't had the neon for long, I'm going to assume it's still tiny and can more than double in size. That combined with the need to be kept in groups, and how active they can be at times (males chasing each other about and the like), would effectivly result them in hitting the sides of the tank constantly later on, or simply sit still and not want to move around due to the small space.


Micro fish like ember tetras will only get to an adult size of a young neon like yours is now, so they would be fine.

 

Neons are very active shoaling fish thats why hun
Bettas aren't as active and like hardly any movement in there tank , they are totally different to neons

my micro raspboras (brigittae) are only just over 1cm in length at full size

 

neons are actively schoaling fish that like to swim up and down a nice long tank, bettas are happy to just sit in one spot,and be alone.

 

I'd kinda disagree with that, some bettas may be like that, but none of the ones I've seen (unless they are unhealthy).

They are relatively small fish though , and a 14L would give more than enough space for them to swim around lots and just generally frolic .

 

If you suspect your other fish died of ntd he shouldnt' be rehomed just yet.
You will have to wait six weeks or he will infect another tank of fish,

 

Female adult neons can sometimes get slightly bigger than 1.5", say 1.75" and females can be a lot bulkier than males. An adult shoal of neons would be very cramped in a 14L, the ~0.5" makes a differance.

A 14L is on the small side for any active shoaling fish, but the slightly smaller ember tetras would behave fine in that size of tank if you already have it.

A 25L would be about the minimum for a group of something like neons, which is again on the small side but should give them enough room to swim around fast when they want to (obviously depending on the number of fish and any other species of tankmates).

Then there's fish like zebra danios that get around the same size, but I wouldn't recommend for a 25L, due to tier hyperactivity .

It just takes experience owning/seeing different species of fish in different situations to form your own opinion, looking at max sizes and using rules like the 1" per gallon rule are very unreliable ways of going about it, especially if you don't have experiance with the fish so don't know how they behave normally.