You know me, take many years to "calibrate " my eyes , i wont use those water test as first option , i go by read the color of the corals , how happy they are, water flow tell you, some, brown, green color tell some, location up or down, etc. In my personal opinion , we have 2 major issue to control.
# 1. .......Detritus.
The faster and safe you exported , the better is ( PO4, NO3 issue)
Constant Alk. also Nitrate.
If some how control the NO3 (constant) Denitrification Sulfur Reactors , works great for me, If some how NO3 is constant to 4 ppm ( in my case) PO4 stay 0.02 to 0.06).
I believe in BIO, healthy water ........show you ...... healthy coral,,,,,,crazy color.
I am so happy , i do NOT use GFO anymore ( list for now).
here is my version of nitrate buster, this is the second unit that I have built to support my new tank, it is all about oxygen free zone where bacteria used this surface area to consume nitrates and turn it in nitrogen gas, more porous media more bacteria..