It depends on the frequency of use, number of people, ambient temperature and quality of water used. In order to keep the water fresh and clear for as long as possible, it is necessary to regularly check the water quality with test strips. All values ​​(pH, hardness, chlorine, alkalinity) should have ideal parameters. If they do not, consult a pool chemical seller and treat the water. If your hot tub has a saltwater system, it converts salt into gaseous chlorine. The saltwater system therefore only addresses the amount of chlorine in the water. It does not affect other parameters (pH, hardness, calcium).