A Hydroponic Growing Medium. A fired-blown clay material that is sterile, lightweight that can used in hydroponics, blended with soils for improved aeration, or as decorative top dressing for container plants. Use it alone in hydroponics or try blending it with Coir or your favorite planting mix for superior aeration. Aerorock is a much better alternative to perlite, in that it will help buffer nutrients and not lose its structure and air holding capacity. General rule of thumb for super charging the aeration levels in soil and coir: Line the bottom of an Aerobag with a layer of Aerorock and fill the Aerobag with a mix of 1 part Aerorocks to 19 parts soil, coir or Amazon Bloom. Indoor/Outdoor plants, soil and hydroponics.