The Waste-Away Time Release Gels employ our specialized bacteria to break down fish waste and other nutrients, resulting in a cleaner aquarium. The gels are easy to install -- simply use the suction cup to attach the gel to a hard-to-reach area with minimal water flow. For best results, pre-treat the tank with our Waste-Away Liquid, then maintain with the Time Release Gels. We offer three sizes of gels, tailored to tanks of 10 gallons, 50 gallons, and 100 gallons respectively, and in both freshwater and marine (saltwater & reef) varieties. Each gel lasts around one month and must be replaced when it turns a tan color.