What caused my SPS whitening at their tips

[linhct]

Howdy friends! My tanks parameters are:
NO3: 5
PO4: 0.04
Alk: 9 (doesnt swing more than 0.5/day)
Mg: 1260
Ca: 430
Salinity: 1025
Temp: 27C (doesnt swing more than 0.5/day).
Recently i notice my red SPS has some white spots on its tips, please see the pic for your reference. Is it going to be bleached?
For the green one, i notice its polyps are not 100% expanded and some of them get brown at the side they are not contacting directly to the light. Should I worry about it? I’m feeding both of them by AF Phytomix every 2 days.

 

[TnFishwater98]

How olds your tank? When did you get the acro?

 

[Steve180]

Picture is hard to see but white tips can be new growth

 

[damsels are not mean]

Usually white tips are good... Means growth. Some always have white tips. I am not aware of an issue where they have white tips as a stress response.

 

[linhct]

Thank you friends!
@Steve180 I hope this is better to see
@TnFishwater98 the tank is 4 month and i added acro 1 month ago