Don't forget, SPS issues like these can present themselves weeks after you had made a change. I had a similar experience and it turned out to be a bad test kit for alkalinity. It was reporting 7.5dkh, when it was actually at 5.5. Had acros STN/RTN and dead tips. Once I got a proper kit and brought alk up to 8.0, things healed nicely. Also, my phosphates are at a .45 (tested yesterday) and my acros are growing fast and have great color. I did add GFO to cut it in half, but I don't buy the whole YOU NEED >.08 phosphates for SPS. Just not the case.
Verify your alkalinity with another test kit. Also, ensure your refractometer is calibrated.
Verify your alkalinity with another test kit. Also, ensure your refractometer is calibrated.