Review on Advanced 3-in-1 PH and TDS Meter Combo: High Accuracy Digital Water Tester for pH, TDS, EC, Temperature, and Conductivity Measurement in Home Drinking Water, Hydroponics, Aquariums, and More by Christopher Smith

First they didn't work out of the box, both devices were with dead batteries. After changing the battery, the TDS monitor EC never showed 0 at startup. Follow the instructions which weren't very good. I had to question the ppm readings. Even my distilled water was high in ppm. My tap water and filtered water from the fridge were all red no matter what. So I'm hesitant to believe this is close to being accurate. The pH monitor showed the same value of 8.1 for all the liquids I tested before and after calibration. So I'm not sure what's wrong with that. So I went to Revain online, hit the return/refund button on my order, repackaged it, took it to Kohl's and shipped it back. I received a refund message the same day. As I have not yet received my invoice from Revain this has yet to be clarified.