Mtoto Zebra Color Change

[Fishkeeper26]

Hi I have been keeping mtoto zebra cichlids for almost a year now, but now their color has turned brown. I know this can mean that they are upset, but idk why. I've kept to my usual weekly pwc, the only thing I can think of is I added a few more shells to the aquarium last week. pH is at 8.2 ammonia 0 nitrite 0 and nitrate 5

 

[HUKIT]

I've seen male msobo turn brown before they turn blue which is normal. Are they always the same color or are they changing intermittently?

 

[Fishkeeper26]

For the past few days they've looked darker