Accu-Tab Calcium Hypochlorite Tablets SI with scale inhibitor, contains 67% available chlorine, designed for use in Accu-Tab feeder. These tabs must be used to keep the NSF approval and the warranty valid. Accu-Tab Blue SI 3-Inch calcium hypochlorite tablets are specially engineered and independently tested by the labs at NSF International to work in Accu-Tab systems in accordance with NSF/ANSI Standard 50. Additionally, these tablets contain a scale inhibitor for clean chlorinator operation and have a blue speckled appearance that differentiates them from other swimming pool tablets. MUST use the Accu-Tab Blue SI 3-inch Tablets with ALL PPG feeders Alert: Important safety information related to swimming pool chemicals Over the past several years NSF has received reports of some chemical distributors supplying chemicals that are either incompatible with the chlorination systems used in swimming pools, and spas or do not meet NSF/ANSI 50 quality standards which verify and certify chemical delivery using a specific system. This can pose potential hazards to your staff and customers. NSF Certifies flow-through chemical feeders to the requirements of NSF/ANSI Standard 50. Feeders are certified for use only with chemicals recommended for use by the manufacturer of the feeder. The NSF Certification of feeders is void if different chemicals are utilized. The reason for this is because using one form of chlorine compound with a feeder designed specifically for another could bring about an incompatibility situation resulting in fire, explosion and/or generation of poisonous gases. Also the potential for inconsistency in chemical concentration resulting from the use of incorrect chemical type, configuration, or brand could result in inadequate or excessive chlorination. Please Note: This product can only be shipped locally. We can not ship outside of Illinois.