Reagent Set for determination of Potassium by the Tetraphenylborate method. Hach Method 8049. Range: 0.1 - 7.0 mg/L K. Set includes: Potassium 1 Reagent Powder Pillows, Potassium 2 Reagent Powder Pillows and Potassium 3 Reagent Powder Pillows for 100 tests.