Garden 
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The short answer: hold free chlorine at 3 to 5 ppm (or bromine at 4 to 6 ppm), keep pH at 7.2 to 7.8 and total alkalinity at 80 to 120 ppm, rinse the filter cartridge every two to three days and replace it every four to six weeks, shock weekly and after heavy use, and drain and refill every four to six weeks. Wipe the waterline each week, and purge the plumbing for biofilm two to four times a year. That routine takes about ten minutes a week plus an hour on change day.
The reason it is more demanding than a pool is scale: 250 gallons at 102°F with two people in it is a far harder chemistry problem than 20,000 gallons at 80°F. We do not physically handle the tubs we rank; our picks come from aggregated owner reviews and expert consensus, described in how we rank, with the ranked field in best inflatable hot tubs.
Target water chemistry
| Parameter | Target | Why it matters |
|---|---|---|
| Free chlorine | 3 – 5 ppm | Below 2 ppm the water is not sanitized at hot tub temperatures |
| Bromine (alternative) | 4 – 6 ppm | More stable at high temperature, less odor, slower acting |
| pH | 7.2 – 7.8 | Above 7.8 chlorine loses most of its power and scale forms |
| Total alkalinity | 80 – 120 ppm | Buffers pH. Correct this before chasing pH |
| Calcium hardness | 100 – 250 ppm | Too low causes foaming and corrosion; too high causes scale |
| Temperature | 100 – 102°F typical, 104°F maximum | The CPSC advises 104°F as the upper limit for adults |
Test at least twice a week with strips, or better with a liquid or digital tester — strips degrade quickly in a humid outdoor cabinet and are the usual reason people think their chemistry is fine when it is not. Always adjust alkalinity first, then pH, then sanitizer.
The routine
Every use
- Rinse off before getting in. A 30-second shower removes most of the lotion, deodorant and sweat that would otherwise become chlorine demand and foam.
- Replace the cover immediately after use. It holds heat, keeps debris out and protects sanitizer from UV.
- Test and top up sanitizer after any session with more than one bather.
Every two to three days
- Remove and hose the filter cartridge, spreading the pleats to flush the trapped material. This single habit does more for water clarity than any chemical. Keep a second cartridge so one can dry fully while the other is in use — a dry cartridge cleans better and lasts longer.
- Skim visible debris and check the water level is above the minimum mark.
Weekly
- Shock with a non-chlorine oxidizer or a chlorine shock per label rate, cover off for 20 to 30 minutes afterward.
- Wipe the waterline with a soft cloth and a spa-safe surface cleaner. Never use household bathroom cleaner on the vinyl — the surfactants foam permanently and some solvents attack the material.
- Full chemistry test and correction.
Every four to six weeks
- Run a plumbing purge product for the stated time, then drain.
- Drain, wipe the interior with a soft cloth and mild spa cleaner, rinse thoroughly, and refill.
- Fit a fresh cartridge and rebalance from scratch on the new water.
The biofilm problem
Inflatable tubs have long, flexible, corrugated hoses and an inflatable wall structure that together present an enormous internal surface area, most of it never touched by a brush. Bacteria colonize those surfaces as a slime layer that ordinary sanitizer does not penetrate — it protects the organisms underneath and continuously seeds the water with new demand. The symptoms are chlorine that vanishes within hours, water that goes cloudy for no obvious reason, and a persistent musty smell that survives a water change.
The fix is a dedicated plumbing purge or biofilm removal product, run with the jets on for the time on the label immediately before a scheduled drain. Doing this two to four times a year, and always when taking over a second-hand tub, resolves most recurring water problems that chemistry alone cannot. It is also the reason a tub that has sat with stagnant water for weeks should be purged rather than simply refilled.
The water change, step by step
The full drain and refill is the one job that takes real time, so it is worth doing properly rather than in a hurry.
- Run a plumbing purge product with the jets on for the time on the label, usually 30 to 90 minutes, the day before or the morning of the change.
- Turn the heater and pump off at the control unit and unplug it before opening any drain.
- Attach a garden hose to the drain valve and run it somewhere legal — not onto a lawn, a vegetable bed or, in many municipalities, a storm drain. Hot chlorinated water kills plants, and discharge rules are jurisdiction-specific.
- Wipe the interior while it is still slightly damp, using a soft cloth and a spa-safe cleaner. A waterline ring that has dried on is far harder to remove. Never use bathroom cleaner or anything with a surfactant.
- Rinse thoroughly and drain the rinse water. Residual cleaner foams for weeks.
- Fit a clean, fully dry cartridge. A damp cartridge reinstalled straight from the hose is a head start for bacteria.
- Refill through a pre-filter if you have hard water or well water — a hose-end filter costs $25 to $50 and removes metals and much of the hardness that otherwise causes scale and staining from day one.
- Balance in order: alkalinity, then pH, then calcium hardness, then sanitizer. Doing it out of order means chasing your own corrections, because alkalinity moves pH and pH moves sanitizer effectiveness.
- Heat and circulate for several hours before use, retesting once it reaches temperature. Chemistry readings taken on cold water are not the readings you will have at 102°F.
A refill takes 45 to 90 minutes for a 250-gallon tub and reheating from cold takes 12 to 24 hours on a standard 120 V unit, so plan the change for a day you will not want to use it. Many owners settle into changing water on a fixed calendar date each month, which is far more reliable than waiting for the water to look wrong.
Common mistakes
| Mistake | What happens |
|---|---|
| Using pool chlorine tablets (trichlor) in the tub | Drives pH down hard and builds cyanuric acid in a tiny volume. Use spa-labeled dichlor or bromine. |
| Assuming a chlorine smell means too much chlorine | It means combined chloramines and too little free chlorine. Shock it. |
| Adding chemicals with the cover on | Traps corrosive gases against the cover underside and the vinyl |
| Leaving the tub full and unheated for weeks | Stagnant warm water is ideal for biofilm. Drain it or keep it sanitized. |
| Relying on defoamer instead of changing water | Masks a dissolved-solids problem that only a refill fixes |
| Never replacing the cartridge | A cartridge that has been rinsed 20 times filters far less than it looks like it does |
| Draining onto a lawn or garden bed | Chlorinated water at 100°F kills plants; check local discharge rules, which are jurisdiction-specific |
One safety note: inflatable hot tubs plug into a standard 120 V outlet and must be on a GFCI-protected circuit, ideally a dedicated one. Do not run them on an extension cord — manufacturers universally prohibit it, and the heater draws close to the continuous limit of a 15 A circuit. Any new outlet is licensed electrical work in most jurisdictions.
For water-change timing see how often to change hot tub water, for filters how long hot tub filters last, and for the running-cost side how much electricity an inflatable hot tub uses and how much it costs to run a hot tub per month. If you are still deciding, are inflatable hot tubs worth it is honest about the trade. Everything else is at the pools and spas hub.