Check out the combo's Hanna has. They do PH and EC, PPM. I tried a TDS pen and a milwake PH pen . They crapped out on me I got the HANNA and been working for months with no problems and don't forget calibration solutions to test pens. Otherwise buy a pool or pond PH test kit with the drops. I keep one around just in case. In hydro PH is king, it must be right. Just remember ( If you go cheap you grow cheap).