Same procedure for Vita Spa and American Whirlpool.
Why drain at all
Over time, dissolved solids build up in the water — minerals, chemical residue, organic material — that no amount of chemical adjustment can correct. That's what makes water look dull, foam more easily, or develop an odor even when it's "balanced" on paper.
How often
Spa gallons ÷ 3 ÷ average daily bathers = days between draining. Example: a 425-gallon spa with 1.5 daily bathers on average comes out to roughly every 94 days. If you're not sure of your spa's gallon capacity, check your owner's manual or ask us. If water stays hard to balance or cloudy no matter what you do, drain it regardless of where you are in that count.
Steps
Turn off power to the spa at the breaker.
Locate the external drain (base of the spa, usually front corner — check your specific model if unsure) and connect a garden hose.
Open the valve and let it drain fully.
While it's empty, clean the acrylic surface — see Cleaning Your Spa's Surfaces & Cover.
Refill through the filter standpipes — see Filling Your Spa for the First Time — and restart your startup process.
Don't turn the heater back on until you've got full flow from the jets for a few minutes after refilling.
Full technical detail: Vita Spa Owner's Manual / American Whirlpool Owner's Manual