One possible grow medium that might be considered somewhat comparable to Hydroton (expanded clay pebbles imported into the USA from Germany) is Buildex, an expanded shale product produced at a quarry located between St. Joseph, Mo. and Kansas City, which is only about 150 miles south of my location near Omaha, Ne. The company sent me a 10 pound sample of the material to test. Today, after several weeks of letting a handful of the material sit in pH neutral snow melt (see attached photos), I tested the water. As you can see, it is on the acidic side, which conflicts with what they told me, that their tests 'several years ago' showed it was more akaline; in the ph 8.6 range.