This is the bit that I don't understand - Rockwool is inert and by definition should not need hours of pre-soaking as it cannot absorb anything - that's it's job; it doesn't react or interact with anything - all it does it hold the sproutling/seedling/plant in place. Although the pH-adjusted water is utterly correct and nigh-on essential. It should be enough to simply ensure the rockwool gets a thorough soaking so that the combined rockwool/water is pH-stable (there's a lot of alkaline rockwool dust inside virgin rockwool). Or am I missing something?
