Stablcal Turbidity Standard, 200 NTU, 100 mL | Hach 2660442 Stablcal\ Turbidity Standard for all Turbidimeters. USEPA accepted for calibration purposes. Stablcal\ Stabilized Formazin Turbidity Standards are true Formazin dilutions developed for use in any turbidimeter. NTU Value: 200. Bottle: 100 mL. Precise, Pre-mixed Formazin Solutions Based on Formazin Primary Standards Enhanced Stability Saves Time and Labor Confidence in results