its a nice piece to read but ''Four different meters test for nitrate, potassium, sodium, and calcium, and they sell for about $400 each.'' is not worth the effort for a simple grower i think if you want a so called kit, also the tests are almost $90 per test if they do it for you..

And they say leaf tissue is old because when you notice anything it means its already happened but i dont see people do tests or let the lab do tests if they dont see any problems at that time...i mean i dont think people would do ''random'' tests just to make sure

This tech could be good for a comercial grower but not for a simple home growing person with just a few plants