How Often Should You Drain and Refill Your Hot Tub?

"How often should I drain my hot tub?" is a question with a confident-sounding short answer (every 3–4 months) and a more interesting long answer that depends on how the spa is used. Here's the version of the answer that actually helps.

The Short Version

For a typical Nashville household — two to four regular users, normal weekly soaks — drain and refill every three to four months. That's a solid average. Some spas need it sooner, some later.

The Long Version: Use-Based Math

The industry rule of thumb is to take your spa's water capacity in gallons and divide by 12, then divide again by the number of bathers per day. The result is the number of days you can run that water before it should be changed.

So a 400-gallon spa used by two people daily: 400 ÷ 12 ÷ 2 = ~17 days. Used by two people twice a week: 400 ÷ 12 ÷ 0.57 = ~58 days. The math is rough, but the point holds: the more bodies in the water, the more often it needs to be replaced.

Signs You're Overdue Regardless of the Calendar

• Foamy water that won't quit. Even after rinsing the filter and shocking, foam keeps coming back. That's high total dissolved solids — drain and refill is the only real fix.
• Sanitizer drops fast. If you're adding chlorine or bromine and the level is back to zero within hours, the water is over-saturated with organics and oxidizers can't keep up.
• Persistent cloudiness. Cloudy water that won't clear despite filter cleaning and balanced chemistry usually means TDS or calcium hardness is too high.
• Funky smell. Healthy spa water smells like nothing. A musty, chlorine-y, or sour smell means biofilm is winning.
• Skin irritation after soaking. Often a TDS or pH problem masquerading as a sanitizer problem.

The Drain Itself Is the Easy Part

What separates a meaningful drain from a wasted afternoon is what happens during the empty stage. Most homeowners drain, refill, and balance. We strongly recommend three additional steps in between:

1. Line Flush

Before draining, add a spa line cleaner per the bottle directions and run the pumps on high for 15–30 minutes. The cleaner breaks loose the biofilm that lives inside your spa's plumbing — the milky-white gunk that built up since the last drain. Without this step, your fresh water will be re-contaminating itself from day one.

2. Wet/Dry Vacuum the Jet Lines

Once the spa is empty (or nearly so), run a wet/dry vac on each jet face for a few seconds. You'll pull surprising amounts of crud out — calcium scale, biofilm bits, sand and grit. This is the step most homeowners skip and most techs do.

3. Shell Wipe-Down

The waterline ring is body oils, lotions, and minerals. Wipe down with a spa surface cleaner (don't use household cleaners — they foam). Pay attention to the headrest area and seat corners where buildup hides.

Refill Best Practices

• Use a pre-filter on your garden hose to strip metals and chlorine from city water. This is especially helpful in parts of Nashville with higher iron content.
• Fill through the filter housing, not over the top of the shell. This pre-primes the pumps and avoids airlocks.
• Let the spa heat all the way up before adding sanitizer. Cold water masks pH and alkalinity readings.
• Adjust alkalinity first (80–120 ppm), then pH (7.4–7.6), then sanitizer.

When to Drain More Often

• Heavy use — daily or near-daily soaks by multiple people.
• Pool parties or hot-tub-as-party-feature with non-regular bathers.
• If you ever have a sanitizer failure (broken cover, week of no chemistry).
• If you suspect a biofilm bloom — drain, deep-flush, and refill solves it cleanly.

When to Drain Less Often

• Very light use (a couple of times a month) with strict chemistry.
• Spas with high-end mineral cartridges or UV/ozone supplements that reduce chemistry load.
• Smaller capacities used by one or two people who shower beforehand.

The Service Option

If draining and refilling sounds like a half-day project you'd rather not do, we offer drain & deep clean as a standalone service. We bring the line cleaner, the wet/dry vacuum, the surface cleaner, and the right starter chemistry — and we handle the whole rotation in a single visit.