I have a small school of tetra neons along with one zebra danio and a white cloud in a 5 gallon tank, I have had fish die before drom swim bladder disease and the like but I can't figure out what this neon had. The belly is swollen but it does not appear to be in distress and no other outward signs of illness are presnt. Anyone have any ideas so I know what to look and possibly treat. I read that it is really difficult to breed neons in captivity but could it be? This happened overnight.

It sounds like you have a female with a belly full of eggs.
It's not really that hard to breed neons.
They often breed inside aquariums and the fish keeper never knows the difference.
Their eggs are tiny and clear and they scatter them wherever around the tank as their swimming.
Some may get fertilized, some may not, and they usually get eaten very quickly.
A breeder uses two tanks so the fertilized eggs survive.

Her belly will stay round until she releases all the eggs.

This is what I believe is happening,
But if the circumstances change or you have any further questions,
Please don't hesitate to ask.

Kae

The swelling in her belly went down over the course of a week but it looks like there's something more wrong with her. Her belly seemed to swell again but it's now focassed in one place and it kind of looks like a blister, like the kind you get on you finger that's all full of water until it's drained. It's just one place and not her whole belly and one way you look it looks like it's full of a clear liquid and another it looks like it might be blood and the bottom is all red looking. She likes to stay at the bottom and has no energy to swim, I just now had to get her free from being stuck between the heater and the glass. She just seems to float when she's not at the bottom.

No need to respond to this question, the fish died. She got caught in the intake of the filter and was gone befre I noticed.