Quote Originally Posted by Herbus
Hey all, just wanted to add something to this quote. Lava rock once it cools, as it ages turns from red to black. It can take hundreds of years to make this change. The darker lava rock is the better it is for inert applications. Very dark or black lava rock is non-toxic (and inert) it is normally more expensive then the red because it is normally below the red in the quarry and more difficult to collect. All aged lava rock is PH stable. Black lava rock is just as good as any other hydro media. Red lava rock is not. Red lava rock can still has trace sulfer compounds that when wetted can cause excess sulfer dioxide. Although sulfer is a trace nutrient in most nutes mixes - excess is toxic to plants.

Herbus
That, is some very interesting information. Thanks for sharing Herbus... very, very usefull.

I'll try and get some of them black aged lava rocks...