The DrTim’s Aquatics NP-Active Pearls are designed to promote optimal water quality in your saltwater aquariums and freshwater or reef fish tanks. These 100% natural pearls eliminate messy, unsightly algae and ensure that your fish tank or aquarium remains free from harmful bacteria. They are available in quantities that include 150 gallons, 450 gallons, 900 gallons, and 3785 milliliters.