m0useanswered grow question 3 years ago use a pen, invest in a descent one, get calibration and storage solution.
there are ph pens for liquids and ph pens for substrates.
can use the liquid one for substrates by gathering up soil and soaking it in distilled water for 24hr. shake for 5 min at the start.
https://bluelab.com/usa/bluelab-ph-pen
nothing but good news from bluelab pens, but they cost a lot. Other shity pens tend to die out in a year or if they get dry.
https://www.nutri-plus.ca/quickcheck_en.html
I use this one, it was only to be temporary but it has proven to be really great. 2+ years still accurate.