Sorry about the loss Jeremy. Its one of my favorite SPS.
For what its worth, I typically notice STN around 0.2 ppm PO4 for SPS but different ones are more sensitive than others.
I am guessing you run some type of PO4 export system like water changes, refugium, skimmer, or GFO. I wonder if PO4 crept up on you, especially after shutting down the skimmer as your system will have to adjust to the change?
For the pH issue, a reverse photoperiod helps out some but its effectiveness is tied to the size of your refugium. The larger, the more effective. Another option is to dose kalk at night. Lastly, you can have your skimmer run at night only to offset some of the pH drop due to buildup of CO2. The skimmer will aerate your water and off gas the CO2 helping to keep your pH from dropping.