Our FROG Serene System is so popular, some spa brands have built it directly into their spas. It makes hot tub care even easier, and your hot tub experience even more luxurious. With FROG Serene, there’s no measuring out the right amount or constantly adding chemicals. You simply replace your FROG Serene cartridges when used up and enjoy weeks of Fresh Mineral Water®. That’s what FROG Serene provides with minerals and a low level of bromine that makes water feel softer and look crystal clear.