
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.

TDS water quality tester - TDS water hardness meter (portable digital salt meter for water analysis)
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Accurate And Versatile Digital PH Meters For Food, Brewing, Hydroponics, Pools And More!
7 Review

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

π Ehdis Digital Manometer: Advanced Precision for Pressure Accuracy
3 Review

π BIAOLING Accurate Formaldehyde Multifunctional Test: Record, Measure, and Inspect with Confidence
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Airthings 2960 View Plus Humidity Sensor
3 Review

π¬οΈ BIAOLING Accurate Formaldehyde Multifunctional Recording: Say Goodbye to Indoor Air Pollutants!
3 Review