Montipora bleaching

[kasen1]

I purchased a monti recently that was half seasons greetings and half mystic sunset. Over the last month about 60% of it has bleached. My other months are doing great.
PO .04
nitrates 9.
ALK 11.
CAL 455.
pH 8.4
Any tips? Sorry for the terrible photos. Turned Blue all the way off for pics.

 

[TX_REEF]

have the parameters changed? That's the most common reason for bleaching - significant changes in water parameters over a relatively short period of time.

 

[kasen1]

They have not changed significantly. I had low nitrates but got them higher over the course of a month. Phosphates were higher but steadily got them down. Nothing over night.