Highest quality Australian Zeolite gravel is the perfect substrate for all ponds. Zeolite improves both water quality and the look of your pond. Zeolite is a natural volcanic product that binds with ammonia and assists to reduce algae growth and improve water quality in fish and frog ponds. It's natural earthy colour suits most gardens and enables you to see fish and tadpoles more easily. Approx gravel size is 3-5mm. Zeolite can also be used in the garden to improve soil quality.