GH pH 4.01 Calibration Solution 8 oz

General Hydroponics® Meter Calibration Solutions General Hydroponics® 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 Hydroponics® technicians check each batch to ensure that our solutions are precisely calibrated and yield reliable readings each time they are used.