Please pay with STRIPE. Our prefered payment provider. Matrix is a highly porous media designed to provide exceptionally efficient biofiltration for single site removal of ammonia, nitrite, and nitrate from freshwater, marine, and reef aquaria. Each liter of Matrix provides over 160,000 cm2 (170 sq. ft.) of surface, equivalent to over 40 L (10 gallons) of typical plastic ball media! This product is sold by volume. Cited weight is minimal weight. Matrix is a naturally mined, chemically inert material for facilitating the growth of biological filtration in aquarium and pond systems. Due to its organic nature - size, shape, coloration, and density of the Matrix material will vary slightly between packages. Any of these variants and small irregularities in sizing are perfectly natural and WILL NOT affect the integrity of the product OR its ability to maintain water quality. It will also not affect pH in the system.