You could be starving your corals. Too clean of a system. Do you test your phosphates and Nitrates? Its a balancing act, I know you don't want to have 0.00. Try feeding your fish more. It may not be the lights, you can try to raise it up another 4 inches so its 8 inches above the water. Also what is your alkalinity? You had a big swing in calcium. Try to keep to the basics. You have a great light, great skimmer, great flow. Just keep the system stable parameter wise (Calcium, Alkalinity, and Mg (if needed)) one week at a time. 10% water changes on a regular basis helps too.Good Luck.