General Hydroponics Calibration pH 4.01 Calibration Solution -- 8 oz
General Hydroponicsâ„¢ uses the highest quality reference solutions, allowing growers to calibrate many popular brands of PH, EC and TDS meters (NaCl scale or the 442 scale). General Hydroponicsâ„¢ technicians check each batch to ensure that our solutions are precisely calibrated and yield reliable readings each time they are used.