Black Polyps on Toadstool Coral

[fishnoob~noclue]

I've been struggling with low nutrients since i started this tank around a year ago. Im not really sure why but no matter how much i feed it doesnt seem to budge. I have mainly soft corals and this is not ideal. Most corals seem to be doing okay but i noticed these black polyps forming on my toadstool. Is this related to low nutrients and if so what can i do about this?

parameters below

Alk : 7.7dkh
Cal: 460ppm
P04: 0
N03: 0
PH: 8.3
Mag: 1500

Thanks

 

[BryanM]

No phos or nitrates?! That's a recipe for dinos and other nuisance issues.

As for the pics, they are blue and it is hard to see what you're focused on. Try taking pics under whites and see if we cant see more detail.