FROG SmartChlor replacement Cartridges for use with FROG @ease Floating Sanitizing System. Kills bacteria 2 ways with a low level of chlorine and FROG Sanitizing Minerals. Minerals last 4 months, SmartChlor lasts up to 4 weeks and flips when empty. Ideal for 600 gallon hot tubs. Uses up to 75% less chlorine* and maintains a consistent low Free Chlorine level, water is Cleaner, Clearer, Softer and Easier to take care of. Uses SmartChlor, a patented chlorine formula that self-regulates on demand for continuous crystal clear water, giving you peace of mind. Flips when empty, making maintenance easy.