All portable hot tubs are built to circulate the water contained in them. You fill them once, and then replace the water based on your manufacturer’s recommendation (typically every 4-6 months). While the water is in the spa it is constantly being purified and filtered. The temperature also remains constant in your hot tub. You set it to the temperature you desire, and leave it there. The only time you would typically need to change the temperature is if you were planning a long period of non-operation. Hopefully, you are starting to appreciate the importance of the water management system and insulation of the hot tub you decide to buy. This will greatly affect the experience and cost of owning a hot tub