Lost A Pleco, But Others Are Fine

[ibuyafish]

Hello all,

Today I just found our pleco sitting on the airstone, I looked closer and realized (s)he was no longer with us. But the other fish are fine, I have five neon tetras and one black skirted tetra. What would cause this?

 

[WILDER]

What are your water stats in ammonia, nitrite, nitrate, and ph.
Was the plec bloated or skinny.