Why turning brown?

[Notsolostfish]

Iv had this milka stylo for sometime now, polyps still extended but as you can see its a bit brown on the right side? Is that normal?

My parameters are the same recently tested

All:8.8
Cal:450
Mag:1410
Ph:8.3
Temp:77-78
Phosphate:0.17
Nitrate:6-9ppm
Salinity:1.025

 

[Uncle99]

Could the polyp to the left, shade that brown part?
Can’t tell in the pic….