I also even just double checked my API Nitrate test kit comparing it to r/o water. It registered zero. So it appears to be working & I trust it because of the way the tank was & is doing. I used it to prevent Nitrates from crashing below 5ppm & always worked for me. I dosed KNO3 to 10-20ppm & left it that way until reset. Then it would always show 5ppms or less after water change. But back then I had more algae to as well. Now with NO algae my nitrates are high! Say 20-35ppm at times with normal Nitrate dosing. So I decided last week to stop dosing KNO3 & to my surprise the levels still stay above 20ppms!