Ultimate filtration. Exceptional ability to remove organic substances. Helps control ammonia, nitrite, and nitrate levels. The color changes when Purigen is exhausted. Purigen is a high-quality synthetic adsorbent that is unmatched by any other filter product. It is not a mixture of ion exchangers or low-capacity adsorbents, but a unique macroporous synthetic polymer that removes soluble and insoluble impurities from water at a rate and capacity that exceeds all competing products by more than 500%. Purigen controls ammonia, nitrite, and nitrate by removing nitrogenous organic waste that would otherwise release these harmful compounds.