Plant!T GMC10L Horticultural Clay Pebbles, 10 Liter, 4mm - 16mm, Natural ClayPlant! T Horticultural clay pebbles are clean, ph stable, and offer great aeration and drainage in hydroponics, especially in flood and drain, deep water culture, and drip feed systems. made from 100% natural clay. Due to their unique structure and ability to cover a large surface area, they offer the ideal environment to foster beneficial bacterial growth around the root zone, leading to naturally healthier plants. 10 Liter Pebble size 4mm 16mm