ORGANIC XL Leca Clay Pebbles Grow Media - Orchids &bull; Aquaponics &bull; Aquaculture &bull; Hydroponics - by Cz Garden Supply (2 LB - XL Clay Pebbles) 2LBS of 100% natural expanded clay. Inert, pH-neutral, clean & decorative. For Orchids - Hydroton's porous structure provides excellent aeration and acts as a water reservoir. For Hydroponics - Ensures good root aeration and prevents rotting, excess acidity and soil pests. XL SIZE 16-25mm - fills approximately: twenty 2" pots, or six 3" pots, or two 5" pots. Only available from Cz Garden Supply (TM); USPTO and Amazon Brand Registry Protected Seed starting heaven! :) 15-25mm pebbles create small pockets of moisture and air Never worry about over-watering and drowning precious seedlings Do more with Cz Expanded Clay Pebbles! Shown in Cz All Star 4 inch Net Pot/Cup Anchorplants for hydroponic grow cycle Blocks light from reaching the hydroponic reservoir Can be reused for several grow cycles Makes moisture and nutrients readily available to plants Serves as an insulator to reduce extreme soil temperature fluctuations Provides the plants with a foundation in which to grow and anchor their roots. Serves to moderate the temperature around the plant roots. Provides a home for beneficial bacteria to colonize. Facilitates the mechanical filtration for the solid waste in aquaponics systems.