Check the listing for details. Grodan Rockwool Granulate 50L Box Hydroponic Rockwool Substrate. Condition: Brand New. Listed at 52.92 USD. Grodan Granulate 50L Box - Hydroponic Rock-wool Substrate Sent with tracking in unmarked packaging Grodan Granulate 50L Box Grodan Rock-wool is an inert plant substrate. A mineral wool made from molten basalt and limestone rock that is spun into cotton-candy like fibresand then compressed into cubes, blocks, or slabs. Being made from natural rock, Grodan is a mineral based product used in hydroponic growing applications. **Recommended use with Grow House Inc. Nutrients and additives ** Grodan Granulate is water absorbent granules of rock-wool (almost flock like). This product is extremely practical for using in hanging baskets, as a stand-alone medium or even as a change from traditional potting mixes. The product is much cleaner to use than potting mixes, has a higher water holding capacity, and can actually reduce watering houseplants to approximately once every 2 to 4 weeks. Directions for use: Pre soak in pH 5.5 water/nutrient before use.