Birdsnest half white

[Reef man 89]

I have purple polyp birdnest from wwc and half is white/ brown and the other half is green with purple polyps I can't figure out why. So I you took the coral and cut it in half from top to bottom only half is green I know that the half that is facing the light looks great but the other half looks like crap my parameters are all in check.
Alk-9.5 (Hanna)
Calcium-420 (Red Sea)
Ph-8
1.025
Po4-0
No3-0
Mag-1350 (Red sea)
The tank is a 40g fusion I am running a reactor with GFO and a protein skimmer I only run the skimmer every couple of days. Hope someone will be able to help me out

 

[Diesel]

Po4-0
No3-0

^^^^^ This is not in check my friend^^^^^^

How long do you have this BN?
And how long is you tank running on the 0.0 nutrients? (more like undetectable).
Any other corals in there?
What about fish, inverts?

IMO reduce the GFO and after a week shut it down, this is causing you problems.
Keep testing daily your No3 as you need to have a save reading of 2ppm at least.
Po4 around 0.04 for now.
Use some dry flake food in your filter sock to bring up nutrients.
What kind of skimmer you have?

 

[Reef man 89]

Thank has been running for 5 months now I have 2 clowns and a goby for inverts I have 1 BCS and 4 turbo snails I started to run GFO about a month ago because my po4 was 3ppm and causing a hair algea problem, after I started with the GFO my po4 went to zero and algea stopped.i know my nitrates should be up alittle but even when I stop skimming and feed more nothing happens. I have a marine pure block broken up in the back chamber so I have a feeling that is causeing 0 nitrate. The skimmer is a Tunze 9004dc that I only run for about 6 hours every couple of days.for other corals I have 6 different types of zoa's, 2 green frogspawn, 2 hammer corals, 1 war coral, and 3 mushrooms all of these coral are growing fast and seem very happy. I feed the fish every other day pellets and a quarter of a frozen cube once a week. For corals I feed them every 3-4 days which is cut up pieces of krill some brine shrimp and some reef chilly. Would u suggest maybe taken out some of the marine pure to try and get nitrates up?

 

[Diesel]

3ppm on the Po4 isn't possible
Maybe you had 0.3ppm.
Yes No3 needs to come up.
you did the right thing to reduce some of you No3 and Po4 but went a little to far.
If you do something in a reef tank to change your parameters you alway have to be on your toes to test for it.