Grodan Rockwool is the leading rockwool company worldwide. Using a base of basalt and limestone, the mixture is heated to 1500°C and then poured onto fast-spinning disks. The result is the highest-quality rockwool, containing only 5% rock content. Because of the low density of the rockwool, it provides exceptional capillary action for the roots, while retaining enough water for growth.
Completely inert, rockwool is ideal for hydroponic growers. It will not buffer the pH of the solution, nor degrade into soluble parts that could affect your plant.
Rockwool must be prepared prior to use, and it is best to soak the cubes for 24 hours in a light nutrient solution that has been pH adjusted to 5.2-6.