This is the complete spa frog sanitising system including:
The cartridges can be turned from 0-6 depending on usage. You need to achieve a 1-2ppm bromine level in your hot tub at a minimum. The more usage your hot tub gets, the higher the setting your cartridge will need to be.
Ensure your PH is between 7.2 and 7.6 to promote bather comfort and sanitiser efficiency.