Skin appears to be receding help on what from

[KRO]

Hello- I have what I think is a Turbinaria Cup Coral (please correct me if that's wrong) and the skin has started to recede in areas and I'm not sure why. I did have it mounted about 6" higher when I noticed the problem and moved it lower thinking it was in a spot the pars where to high but am not sure if that was the problem so reaching out for all your thoughts

Tank details-180 Gal, 1.5 years old, Cal 360, Alk 8.5, Sal: 1.025, Temp 77F, P04- .05, NO3 .5 ppm

 

[T-J]

I can't tell if it's a cup or chalice coral. I've found that my chalice likes significantly lower light. I think cup corals are the same (or more "moderate" light).
Your calcium should be around 420, and you should also increase your Nitrates.