is this a glow light tetra egg

[Jory]

Doesn't look like a platy egg. I've seen platy eggs (stillborn to be more precise) before. Definitely tetras.

stillborn platy eggs are orange. and pretty gross.

 

[Lupin]

stillborn platy eggs are orange. and pretty gross.

That's why I did say they're not platies since I have seen their stillborn fry in my experience.

OP pointed out he has ramshorn snails. Snails leave slime trail around and most unwanted objects can stick on the slime trail from poo to eggs. Not unusual for the egg to get stuck on the glass if it happened to stick on the slime trail.

 

[Lupin]

Is it stuck to the glass? Don't GL tetras scatter their eggs? I think it is a snail egg, or eggs.

The photo does not indicate snail eggs and ramshorns do not lay eggs individually. The egg also has a fry at the left side developing. Note that the egg was individual, not a cluster with dozens of eggs inside it. The only snails that would lay individual eggs are assassin snails and the OP never admitted he has assassin snails. Even then, assassins are still expensive and still command a high price for inch sized snails.

OP did not indicate when he has started seeing his glowlight tetras breeding around so you can assume the egg is days old already otherwise the egg will not appear like the one shown in the first post and should practically be empty prior to being laid.

 

[sun catfish]

and now the egg isn't there