Starting up a hot tub: fill, balance, then sanitize

1. Fill with fresh tap water through a pre-filter, no more than half softened water.
2. Add a sequestering (stain and scale) product and let it circulate at least 30 minutes, or as its label says.
3. Test alkalinity, pH and calcium hardness.
4. Adjust alkalinity first, then pH, then calcium. Hot Spring sets alkalinity to 80 ppm and calcium to 100 before pH.
5. Wait, retest and adjust again. Master Spas says 15 minutes; Bullfrog says 6 hours for balancing chemicals.
6. Add sanitizer once the balance holds, and stay out until chlorine falls to a safe level.
7. Heat to your set point with the cover on.

Each step changes the next. Alkalinity sets how pH responds, so fixing pH first wastes chemicals when alkalinity then drags it off again; Bullfrog says to set alkalinity even if it throws pH further off for a while. Sanitizer goes last because high pH weakens it: above 7.5, Master Spas notes, less than half the free chlorine is active.

Test sanitizer every day. Hot Spring says the first month is for learning how much sanitizer your household uses, so you can set a routine. If the tub won't heat or the jets sputter after filling, an air lock is the usual cause: see weak hot tub jets. For the list of what to buy, see hot tub chemicals you need.