Time for an update...
Parameters:
NO2 - 0.01ppm (Salifert, read from side)
NO3 - 0.2ppm (Salifert, read from side)
PO4 - 0.03ppm (D+D High Sensitivity)
Bro Izzat, perhaps the artificial rocks are releasing PO4... in very small quantity... will introduce some form of PO4 removal this week