I along with a lot of other people have had some issues with the Hannah cal checkers. I suggest another opinion on that level.. Fwiw I sold mine pretty quickly after I got it.. Notoriously wrong readings on the same sample of water.. I have had good luck with the alk (until it's the last few tests in the liquid) and p04.. Tank looks awesome so far
easy to use and i like the digital reading easier then the color chard
ill take a water sample to the store see what they get