Strange black substance coming from pagoda heads

I bought a green pagoda coral about three weeks ago, it acclimated fine and had all of its heads out in about a day's time. Then today I noticed that it had this weird black or really dark green, stringy substance coming from some of the heads, its not coming from all of them just about a third. Does anyone know what it could be? I 'm kinda worried cause I don't want to lose it, all the other corals in the tank are fine, it has moderate flow with good lighting and its placed about middle of the tank. The water param are fine and have been stable the entire time that the coral has been in the tank. I also dose Phytoplankton about three times a week for it and my derasa clam.

 

Expelling waste or zooxanthellae.

 

If it is expelling zooxanthellae is that a bad thing?

 

No not really, if the coral maintains it's coloration I would not be worry at all. Sometimes I believe they just swap out one type of zooxantheallae for another. Just speculation. But no I would not be worried.

 

My open brain/trachy/wellso (whatever ya wanna call it) does this too... out of its mouth hole.. Its like he is pooing.. Color is still great watched mine do it on a few occasions now... Id say its normal..

 

Yup it's pooping!! My Fungia does it all the time and what's really gross is my sexy shrimp love to eat it up! LOL