What is Reddit's opinion of Hanna Instruments HI98103 Checker pH Tester with Ph Electrode and Batteries, 0.00 to 14.00 pH, +/-0.2 pH Accuracy, 0.1 pH Resolution?
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By popularity on Reddit, this product is:

#10 in Substance Analysis Instrumentation

I bought one of these and you can calibrate it (by buying 4ph and 7ph solutions).

Works well.

You’ll need a ph meter like this one. Hanna Instruments HI98103 Checker pH Tester with Ph Electrode and Batteries, 0.00 to 14.00 pH, +/-0.2 pH Accuracy, 0.1 pH Resolution https://www.amazon.com/dp/B0085WOIMQ/ref=cm_sw_r_cp_api_i_1C5B9WJ4X81X24209CVQ

I use a Hannah Probe and stick it into the whey. The are about 30 bucks. Work very well.

< $50

$100 - $200

< $50