
Use these to calibrate one of the cheap yellow PH pens shown here. I used to buy a new Ph Pen every growth streak, but now I can just calibrate it and save money in the long run.

Digital PH Meter Tester - Tiaoyeer Water Quality Tester With ATC, 0.01PH High Accuracy, 0.00-14.00 Measurement Range, 0.01 Resolution For Drinking Water, Aquarium, Swimming Pools, Hydroponic
8 Review

Portable digital multimeter with sound continuity and thermocouple (electric tester) LTX DT-838
7 Review

Efficiently Test Your Antifreeze And Battery Acid With A 3-In-1 Refractometer
18 Review

80 Pieces Water Test Litmus Strips Litmus ph Paper Soil Acidity Meter Liquid pH Tester 1-14
10 Review

๐ฌ๏ธ Advanced 3-in-1 Indoor Air Quality Monitor with CO2/RH/Temp Data Logging and Audible Alarm - NDIR Sensor Technology
8 Review

๐ Enhanced Precision with Backlit Professional Manometer for Differential Ventilation
6 Review

๐ง UEi Test Instruments DAFM3B Digital Multimeter
6 Review

๐ Dioxide Controller for Digital Gas Monitoring
5 Review