New hot tub startup: fill and balance
Filling a new (or freshly drained) hot tub is the one time you balance from a blank slate, and doing it in the right order saves you from chasing your tail later. The whole sequence is: fill, balance the minerals, then sanitize — in that order, because each step sets up the next.
Step 1 — fill (and know your volume)
Fill through the filter housing if your model recommends it (it helps purge air locks). Most home tubs hold 300–500 gallons — find your exact number in the manual, because every dose from here on scales to it. If you have hard tap water, filling through a pre-filter saves you a calcium-hardness battle later.
Step 2 — get the water moving and warm
Run the pump to circulate, and let the heater bring it toward soaking temperature. Chemicals disperse and read more accurately in circulating, warmed water — testing a cold, still tub gives you numbers you'll have to redo.
Step 3 — balance, in order
- Total alkalinity → 80–120 ppm. The buffer that holds pH steady; set it first.
- pH → 7.2–7.8. With alkalinity in range, this usually lands close already.
- Calcium hardness → 150–250 ppm. Too low foams and is corrosive; too high scales. Soft tap water often needs calcium added.
This is the same alkalinity-before-pH order you'll use for every future adjustment — startup just does all three from scratch.
Step 4 — add sanitizer
Only once the minerals are balanced, bring sanitizer into range: 1–3 ppm free chlorine or 2–4 ppm bromine. If you're starting a bromine tub, you establish the bromide bank first, then activate it. Sanitizer works best after pH is set, so this comes last.
Let everything circulate and re-test until all readings sit in range before anyone gets in. A brand-new fill can move over the first day as chemicals fully mix and the water reaches temperature — re-check before that first soak rather than trusting the startup reading.
Step 5 — note your refill date
Spa water has a working life. A common rule of thumb is to drain and refill roughly every 3–4 months (sooner with heavy use), because dissolved solids build up and eventually no amount of chemistry brings the water back. Noting the fill date now tells you when that clock runs out.
| Setting | Startup target |
|---|---|
| Total alkalinity | 80–120 ppm |
| pH | 7.2–7.8 |
| Calcium hardness | 150–250 ppm |
| Free chlorine | 1–3 ppm |
| Bromine | 2–4 ppm |
Soak walks a new fill from empty to soak-ready
Enter your tub volume once; Soak gives the exact dose for each startup step in order — alkalinity, pH, hardness, sanitizer — and tracks your refill date. Pay once, no subscription, no ads, fully offline.
Sources
- TroubleFreePool — PoolMath formulas and target ranges
- Industry spa-care guidance on first-fill order (balance minerals before sanitizer) and refill cadence
General guidance, not a substitute for your own testing and your tub maker's manual. Targets and doses scale with your exact volume — re-test before the first soak.