Ph meter. Guys im looking bullet proof ph meter/pen/what ever :) top quality/price range. I always using bluelab ph meters, but they died after 2 years everytime...
https://www.pnwgardensupply.com/product/gh-ph-test-indicator-8oz/ ... Lol it's cheap. But it always works never needs calibration and you can buy like 10 bottles for the price of one blue lab ph pen.