bubble coral

[68shelby]

My bubble coral has gone into withdrawl the last week or so. it use to be about 8" across and now barely comes out of its skeleton. All other corals are doing fine, the only thing Ive noticed different in any other corals is I have a plate coral that had been extremely light (almost bleached looking since I put in 14k phoenix bulb 4 months ago) has gained backed his darker color over the same period my bubble coral has withdrawn. Could my lights have changed enough to cause a bubble coral to withdraw like that? He is about 20-24 inches deep and off to the side of my metal halide 150w. The plate coral is about 6" above him. Water parameters test good. temp has not been fluctuating. he is pictured in the bottom right. this is when he was full.