New to corals - what’s up with these CC frags

[CDarby67]

Hi,
My step son is establishing a new 20 gal ling marine aquarium.

He has been impatient (yep disaster looming).

He has a frag (or two that he split) of Candy cane coral (kryptonite).
they are placed in the sand directly.
Theee appears to be a “bubble” or egg like growth. It is below the poly and between the polyp and the sand - looks black and shines.

Can anyone tell what it is?
Thanks,
Clint

 

[mangus]

That appears to be bubble algae, if it is an emerald crab would be a useful addition to your tank