Gold Label Hydro clay pebbles are manufactured using a mix of the best quality pure clay and are baked in an open furnace using high-grade clean fuels, guaranteeing absence of heavy metals or other contaminates. Gold Label Hydro Korrels proudly carries the RHP certification for horticulture quality. The unique uneven shape of the pebble is an ideal surface for roots and beneficial bacteria. The porous structure has a high water capacity and is suitable for both ebb and flow and top irrigation systems. Do a side by side with your current grow rocks and you will never go back.