Moon favia excretions?

Have had my moon favia for about a month now, and it has seemed to be doing okay, with a small noticeable amount of tissue growth. However, just today I was gazing at my tank and noticed that it was excreting small little black bits of matter from it's mouths'. Each polyp probably excreted around 10 or so of these black pieces of matter (very small, less than 1mm in size). The coral still seems to be doing okay however, just don't know exactly what that whole little thing was about.

 

Mine has done that before also. Don't know what it is either but it has never affected my coral.