I bought these to check the peroxide levels in our hot tub which we sanitize with hydrogen peroxide rather than toxic chlorine. They work very well. I have a consistent reading between 50-100ppm which is very good. Just to make sure they work I tested one of them in a glass of tap water and it didn't discolor at all which showed me they give accurate readings. The price is also very fair.
Efficiently Test Your Antifreeze And Battery Acid With A 3-In-1 Refractometer
18 Review
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
8 Review
80 Pieces Water Test Litmus Strips Litmus ph Paper Soil Acidity Meter Liquid pH Tester 1-14
10 Review