Need a new PPM pen

[Jungle]

@Tylersays

Anybody got any feeling about this set?

Not very accurate. See my post

Vivisun pH pen - iffy results, not real accurate

I have both a Milwaukee pH controller[1] and a Vivosun pH pen. I calibrate the Milwaukee using GH pH 7.0 and pH 4.01 standard control solutions. Recently, the pH in my reservoir has been gradually decreasing when prior it was always gradually increasing. I try to keep it at 5.8, and recently it’s been at 5.7 (and reasonably steady). This morning it was at 5.5 and I got a bit worried (all values as displayed on the Milwaukee). The Vivosun pen read 5.2. So I calibrated the Milwaukee and it w…