my 0.02.

Concentrate your efforts on water chemistry and bugs

1. Alk
2. Rate of Alk change of the day
3. Look for bugs at day and night time
4. Mag Levels - Required to maintan your alk level
5. Calcium to be in the appropriate range

You lighting does affect corals but I dont think causes death. It causes the corals to loose color or gain color - And under prolonged over/under lighting can cause death.

Untill you identify your root cause dont make too many changes other wise it will cause your SPS to RTN.

I hope it helps.