Help, dont know what happen to my Duncan coral.

[Lyss]

That's a nice colony, mine was on the rocks for a while but put it on the sand a couple years ago. It's doing well on the sand also. As long as it's not buried should be okay.
I just think the op's is not getting the light it needs. For that, I say move it up some.

Yeah my comment was thinking about not enough light being on the sand.

Also the OP has cyano rn so prob not great for it to be on the sand from that perspective as well.