Skirt colors turning brown, only affects certain colors

[anygiven60]

For the past two months I've had a few colonies of zoas that have an orange or yellow skirt turn a brownish color. At first I thought I was missing some trace elements and had an ICP test done which didn't indicate I was missing any trace or major elements. No changes to lighting or flow. Any ideas would be greatly appreciated.

ph 8.2
alk 9
cal 440
mag 1400
phosphate .089 ppm
nitrate 6ppm
78-80
1.026

 

[PDR]

How long have you had the zoas? Have you run any carbon recently?

 

[wattson]

What types of lights are they under ?

 

[anygiven60]

Each colony I have had for four-five months. No additional carbon than what was already existing. Currently under Radion XR G4 Pro. No changes in intensity or schedule of lightning.