WAT4330WTW Phosphate (PO4) Water Test Kit Round Cuvette 16mm. Measuring Range : PhotoLab - 0.5 to 25.00mg/L (PO4-P) 0.5 to 25.0mg/L (P Total) 1.5 to 76.7mg/L (PO4) PhotoFlex - 0.5 to 15.0mg/L (PO4-P) 0.5 to PK25