Hi Guys, my Trident NP still read PO4 as Zero.
None of my test kits show any PO4 level too. Salifter, Sera, Red Sea & Hanna Checker (I have the ppm one, not the ppb one).
So I have no choice but to Calibrate NP with my own water which is 5ppm + Zero PO4.
NO3 is now consistent with my Hanna...