Purple Bonsai slightly browning out

[Scubabum]

I've had a Purple Bonsai for about 3 months. Over the last two day it has gone slightly brown. The yellow polyps are still extending. First thing I thought of was PO4. I checked this morning with Hana checker and they are reading 0. Any thoughts or help would be greatly appreciated.
Ph 8.2
Salinity 1.026
Alk 9.5
Cal 435
Mag 1300
Nitrate 2ppm
Phos 0
Lighting is a Kessil AP700 38% at Peak mid day.