Aquasafe ?

[Willito]

LostMind, it seems like an expensive hobby for you just to obtain clean water. Changing filters every month is something I'd hate to deal with

Deb, TSD meters, and eletronic measuring devices alike, are tools that require period calibration. I have little trust in them myself. Their readings are highly dependent on the calibration as well as the power supply. IMO, the human senses are sometimes a better tool.