WAT4328WTW Phosphate (PO4) Water Test Kit Round Cuvette 16mm. Measuring Range : PhotoLab - 0.05 to 5.00mg/L (PO4-P) 0.05 to 5.0mg/L (P Total) 0.2 to 15.3 mg/L (PO4) PhotoFlex - 0.05 to 3.00mg/L (PO4-P) 0.05 PK25