Nature2- Nature2 uses minerals to sanitize the water. Using a Nature2 system on your pool can dramatically reduce the amount of chlorine/bromine you use. For a traditional chemically treated swimming pool, chlorine usually needs to be maintained between 1-3 ppm. With a Nature2 system, you only need to maintain a chlorine/bromine residual of 0.5 ppm. The minerals are introduced to the water as it passes through a cartridge (plumbed "in-line"). The cartridge does have a life span and needs to be replaced every 6 months or so. Nature2 offers a variety of different systems for all pool types and does not require any electricity to operate. Remember, Nature2 is designed to lower the amount of chlorine/bromine you need for your pool, it does not replace it.