Since you grew in water, then you must have a digital ph meter? Like stated above, do not buy the probes-they are shit! If you want to test the soil then you will have to pay to play. Good soil testers are not cheap. So what we/I do is test run off. Water plants until it comes out the bottom and then water some more. Then take your ph probe and test that water. That's your ph, give or take a tad. Then just add ph up or down to water\nutes and away you go.