Po4 and no3 is a compound. Its chemistry
Now nutrients in our hobby is more organic and inorganic nutrients
What your skimmer pulls out is the stuff that will brown acros if you know what I mean.
I have a 85g or so total volume tank running a helix 5000 skimmer at 6000Ml of air.
This is how I control the unwanted "nutrients organic or inorganic" from turning my corals brown.
Now the color of coral is dependant on the zooxanthellae algae in the coral.
You want color than provide it with the proper amount of no3 and po4 with minimal "nutrients"
It will shade itself from the UV of the lighting which what we see are the awesome colors.