The nature 2 spa cartridge is a great way to reduce the amount of chlorine (it is NOT compatible with bromine) needed to keep a spa properly sanitized. When used in conjunction with an ozonator it can possible to reduce the amount of chlorine needed to sanitize a spa to as low as .5ppm. It also gives the water a softer feel, and is gentler on your skin as well. The Spa Frog is very similar to the NaTure 2 Spa Cart and can be used with Bromine as well. It works the same way as the Nature 2 for the pools work(if you are familiar with that).
Jason,
Store Manager for a D-1 & Caldera dealer