Patchy coral

[Mike1885]

Hi, I'm Farley new to keeping sps, I Woke up yesterday and noticed a single white patch on my stag coral after it being in the tank for just over a week, thought nothing of it and did my weekly 15% water change.
Woke up this morning and there's dead patches all over it!!
All parameters are within there range.
Anyone know what this could be or had a similar experience?
Thank.

 

[Scorpius]

aefw? Looks like bite marks.

 

[Mike1885]

I've just noticed my Xanthid crab(dark green red eyes) crawling away from it as
I walked near the tank
Could this crab have anything to do with it?
Thanks

 

[cubman20]

yep i found two crabs on mine i got them out at night when they were in the act