Terra Clay Pebbles (40 Liters) - Includes a free 2&rdquo; x 3-1/2&rdquo; Measuring Conversion Chart Magnet Extremeley stable in both pH and EC Made from 100% natural clay Strong structural integrity means that they are less likely to break and compact, which helps to prevent dripper systems from getting blocked Pre-washed to aid in stability Drain freely and do not hold any excess water, providing good oxygen levels around the root; suitable for flood and drain systems, multi-pot and drip feed systems