Goni skeleton turning brown

[Jintea]

Recent change from tap water with high phosphates (3ppm on salifert test!) To rodi water...goni was looking awesome under the tap water...even after change phosphates floated around 1.5 then down to 1 after about 2 weeks of water changes..

Params.
Temp 78
Sg 1.026
Mag 1420
Cal 400
Alk 8.6 (low today, is generally around 10.5)
Phosphates 0.25
Ammonia 0.25 (just pulled out a dead goby)
Nitrite 0
Nitrate 5

Is this reversible? What causes it? I have another goni that is looking great

 

[Jintea]

No polyp extension in about 2 weeks although parts look like they are trying to