I’ve heard people mention ‘lava rocks’ as a grow medium, instead of Hydroton. Are they talking about special lava-rocks sold at a grow store, or the red lava-type rocks used for landscaping, that people use in their front yard in place of grass ? The yard kind is probably very cheap compared to Hydroton (they probably sell it by the cubic yard like soil). What I wonder is: 1) does it release minerals into the solution that would raise/lower the pH ? and 2) does the rock being red mean it’s got a lot of iron in it, which is toxic to plants (except in micro dosages) ? Has anybody grown in red yard rocks?