Chemi-pure is the original formula for over 50 years with millions of satisfied customers. It was invented by Dick Boyd in the 1960's. Chemi-pure combines high grade granular activated carbon with advanced ion exchange resins Offering superior filtration for your freshwater, reef, or marine aquarium. Together, this proprietary blend removes odors and color- causing dissolved organic molecules along with toxins, medications, phenols, and dissolved metals. Chemi-pure's exclusive media formula has an ideal pore size for absorbing nitrogenous wastes and dissolved organics in your aquarium water while being the safest filter media available. Chemi-pure will keep your aquarium healthy, stable, and crystal clear. Keep chemi-pure sealed in container until ready for use. Rinse lightly under running water then place nylon bag in any external power filter, canister filter, or filter sump. Chemi-pure should be replaced approximately every 3 months depending on bio-load. If more than one chemi-pure filter bag is used, change one at a time Every week until all bags have been replaced. Use one 6.5 oz. Unit for up to 25 gallons. Pack of 2