General Hydroponics TDS Calibration Solution 1500ppm (8oz) $6.98 General Hydroponics pH Calibration Solution (8oz) $6.98 Genisis pH 4.01 and 7.01 Calibration Kit (16oz) $22.00 General Hydroponics pH Control Kit $15.98 General Hydroponics pH Test Kit $6.98 General Hydroponics pH Up (qt) $12.98 General Hydroponics pH Down (qt) $12.98