Balance at hot tub temperature
Spa Calc's CSI gauge uses your tub's temperature, because hot water pushes water toward scale. It sits next to the soak check, so you see both whether it's safe to soak and whether the water is balanced.
Hot tub routines
Spa Calc logs soaks with how many people and how long, gives a top-up after each one, tracks filter rinses on inflatable-length schedules, and counts down to drain day from your tub's size and use.
A log for the tub
Every test, dose, soak, drain and filter rinse goes into Spa Calc's log, with charts up to a year, free for one tub.