Sustain 3-inch blue chlorinating tablets, when used according to label directions, will keep your swimming pool looking great by providing routine sanitizing power all week long. These tablets contain a proprietary erosion modifier that allows them to deliver chlorine more consistently than conventional white tablets (Trichlor). And, Sustain Tablets don’t contain cyanuric acid (CYA) which can inhibit chlorine effectiveness. The skimmer dispenser cup packed inside every bucket allows you to control just the right amount of chlorine for your pool with an easy-to-use adjustable lid.