I've noticed alot of people use pool pH test kits for pH and that provides reasonable accuracy and it's cheap, so most can be satisfied. Others would like a research grade instrument until they see the price. There is an option for under $100, (albeit barely) it's called a pH turtle from Hanna Instruments and it's actually a pH measurement interface for a computer. it is capable of data logging, temperature correction and quite a bit more. All you need is a computer. (which all on the board have) If you have a laptop you can even take it down to the pond. Info can be had from Hanna Instruments Accurate pH, reasonable price, necessity....

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