Grodan Rockwool Slabs are a perfect addition to gardeners familiar with drip and ebb & flow hydroponic practices. These rockwool slabs are designed to fit into 15/75 trays which easily integrate into existing drip systems. By making use of pH stable, fully inert media like Rockwool, …gardeners have complete control over the nutrient schedule and water feeding of their plants. Rockwool is created by spinning molten rock into fibrous, almost cotton-candy like material then pressing that product into blocks, cubes, slabs, plugs, and every other indoor gardening shape. Shop now in HTG Supply’s wide selection of Rockwool slabs.