The industry’s standard formula to determine

When to change spa water, here it is

Gallons in spa ÷ 3 ÷ average daily bathers = number of days between draining s. For example, if you have a 500-gallon spa with an average daily bather load of two, the formula would work this way:  500 ÷ 3 = 166.66 / 2 = 83 days According to the formula, this particular spa’s water should be drained and changed approximately every three months.