WAT4332WTW Phosphate (PO4) Water Test Kit Round Cuvette 16mm. Measuring Range : PhotoLab - 1.0 to 100mg/L (PO4-P) 3.0 to 307.0mg/L (PO4) PhotoFlex - 1.0 to 50.0mg/L (PO4-P) 3.0 to 153.0mg/L (PO4) PK100