Neon Tetra With A "black Eye"?

Over night I noticed a neon Tetra has a black eye or growth. Any ideas what it is?

Also. With only 5 neon tetras (now 4) and 1 Pleco. Mysteriously a Tetra dissapered one day (no, there's no other way how on earth he could have dissapered) it's unexplainable.

Just wondering what on earth would have caused the black eye and maybe any ideas why a Tetra would disappear?

 

Hmmm, it could be from injury, a mad dash across the tank and hitting an object in tank or the side glass. It looks like accumulated blood, like a bruise.

 

That's what I thought at first, a bruise. But then I was thinking if one Tetra disappeared maybe another Tetra or the Pleco must have done something.

The bruise looks quite bothersome m. I think he has a limited amount of time left to swim before he turns his belly up.
Could it be from black moss? I have some reoccurring moss on one of the rocks.

 

That's what I thought at first, a bruise. But then I was thinking if one Tetra disappeared maybe another Tetra or the Pleco must have done something.

The bruise looks quite bothersome m. I think he has a limited amount of time left to swim before he turns his belly up.
Could it be from black moss? I have some reoccurring moss on one of the rocks.

No, it would not be from black moss.

 

Poor guy. Must have poked his eye on something than. Thanks for the help!