You said par was at 135? That's not enough to cause issues you describe. I think this is absolutely a water chemistry issue with swings in some things and the phosphate bottoming out. Keep target feeding and let the phosphates come up to about .08-.1
I would also bump the Mg up faster. Just get some epsom salt from the drug store for this. You can go up by 100ppm a day without any issue.
https://reef.diesyst.com/chemcalc/chemcalc.html
I would also bump the Mg up faster. Just get some epsom salt from the drug store for this. You can go up by 100ppm a day without any issue.
https://reef.diesyst.com/chemcalc/chemcalc.html