“A better investment is to purchase a digital pH reader. Amazon sells a KETOTEK digital pH meter for $15, and the VIVOSUN pH meter with TDS meter combination sells for $20. But despite the higher price tag, the Dr. Meter pH100-V that Amazon sells is easily one of the best pH readers on the market for hydroponic gardeners. At $40, it costs twice as much, but it comes with easy to use instructions, automatic calibration, and offers pinpoint accuracy. Investing in a digital pH reader means never running out of test strips or purchasing more pH Test Indicator ever again.”