This Pro-Carb Activated Carbonis fast acting, long lasting and designed to keep your salt or fresh water aquarium crystal clear for up to 4-6 weeks. Carbon removes harmful chemicals, toxins, odors, discolorations and other contaminants. Recommended for use in Cascade, and all other hang-on internal and canister filters. Penn Plax Inc. has been in the business of making quality and innovative pet products for over 50 years.