Duncan coral not opening

Hey everyone, I have a Duncan that's been in my tank since last January and has grown from 2-3 heads to at least a dozen. The last couple weeks however it hasn't really opened up much. It's either been nearly completely closed or opened just enough to make out its arms. It's been in the same spot on the sand bed since I added it 15 months ago until recently i switched it with a Torch coral (also on sand bed) that's been having the same issue lately.

My parameters are:

pH: 8.0
Ammonia: 0
Nitrite: 0
Nitrate: 10
Calcium: 480
Mg: 1350
Kh: 12
Phosphate: 0.25
Salinity: 1.023

Any suggestions?

Oh, I have an Orbit Marine Pro LED lighting system that's been on the aquarium (a 29 gallon Biocube) since sometime around last November.

Thanks