Purigen is a premium synthetic adsorbent that is unlike any other filtration product. It is not a mixture of ion exchangers or adsorbents, but a unique macro-porous synthetic polymer that removes soluble and insoluble impurities from water at a rate and capacity that exceeds all others by over 500%. Purigen controls ammonia, nitrites and nitrates by removing nitrogenous organic waste that would otherwise release these harmful compounds. Purigen's? impact on trace elements is minimal. It significantly raises redox. It polishes water to unparalleled clarity. Purigen? darkens progressively as it exhausts, and is easily renewed by treating with bleach. Purigen? is designed for both marine and freshwater use. This product is sold by volume. Cited weight is minimal weight.