Hydrolite grow media amendment has a unique, porous design that retains nutrients and delivers them slowly over time to plants to drastically improve overall growth. It also improves aeration when mixed with soil, coconut coir or peat-based mediums. Hydrolite is 70% silicate volcanic material and is also derived from fish meal, composted seabird guano, kelp, rock phosphate, potassium carbonate, and calcium carbonate. This reusable medium doesn’t float and is available in either 4-6 mm or 15-20 mm diameters. Great for use in soil and other media, and for slow release of nutrients in hydroponic systems.