Goniopora issue

[USMA36]

Can anyone help me figure out what’s up with my Goni. Was super happy 6” polyps with giant heads. For the last few months it has retracted. There’s a brown substance on it that doesn’t seem to be spreading but it’s closed up most in that area. Water parameters haven’t changed. Alk 8.5 controlled via trident. Nitrates 10 - 15 phosphate .08 to .12.

 

[Lavey29]

Some say the green ones are difficult to sustain long term not sure why. I have the same one 1.5 years now and it has started doing similar. The red and purple ones are still full bloom extensions though.