Duncan coral with light ridges?

[indiana812]

Long story short, went out of town for a week and came home and my duncan coral was obviously irritated.
After multiple mass water changes, I have had my parameters stable to prior vacation.

I have recovered everything back to pre-vacation happiness with the exception of my duncan.
I iodine dipped it today so it’s still agitated, but the light ridges around the duncan heads is what I am curious about, besides my perimeters (I don’t have them with me at the moment) - is this something that is a sign of a disease or that I should be worried about?

 

[blaxsun]

Does it normally like being in the sand bed? Mine prefer higher elevations.

 

[indiana812]

Tbh I’ve had it everywhere but in December I bought an RBT & they are still getting settled due to the numerious splitting thag has been going on. I think I realized that it was the skeleton of the duncan possibly so I mixed it back to the back wall with less flow to
hell ease the recovery. We will see how it goes !