Quick Answer: For a hot tub you need five things: a sanitizer (chlorine dichlor granules or bromine tablets), a pH increaser and decreaser, a total alkalinity increaser, an oxidizing shock, and test strips. The easiest path for a new inflatable or plug-and-play tub is a spa startup kit plus a box of AquaChek test strips. Bromine is the more forgiving sanitizer at hot-tub temperatures; chlorine is cheaper and faster to dissolve — pick one and never mix them.
Last updated: July 28, 2026 — added the pH/chlorine effectiveness math and the Pseudomonas incubation window below.
Clean hot-tub water is almost entirely about chemistry, not scrubbing. Get the balance right and the water stays clear, odor-free, and gentle on your skin and your tub’s liner. Get it wrong and you get cloudy water, itchy skin, or a slimy biofilm. Here’s exactly what to buy, what each product does, and how to keep it simple.
Hot tub chemistry by the numbers
- 3 ppm is the minimum free chlorine (or 4 ppm bromine) the CDC says hot-tub water must hold to reliably kill germs — the single number that keeps you out of the “hot-tub rash” statistics.
- 7.2–7.8 is the safe pH window; drift below it and acidic water corrodes heaters and liners, above it and sanitizer stops working and scale forms.
- 80–120 ppm total alkalinity is the buffer that keeps that pH stable, per standard spa water-care guidance — get alkalinity right first and pH mostly behaves.
- 2–3 times a week is how often you should test, because a small ~300-gallon inflatable heats and gets used hard enough that chemistry swings faster than in a big in-ground spa.
- Up to 75% less chlorine is what the maker of the FROG @ease system rates its SmartChlor cartridges to use versus traditional dosing — the appeal of a drop-in sanitizer for hands-off owners. A hot tub ozonator is the other common way to cut sanitizer use, manufacturer-rated at up to 50%.
- 53% vs. 22% is the swing in chlorine’s active (germ-killing) fraction between pH 7.4 and pH 8.0, per public-health water-chemistry guidance — the reason this guide’s 7.2–7.8 target isn’t arbitrary: drift just half a point high and roughly two-thirds of your chlorine’s killing power is gone even though the test strip still shows “sanitizer present.”
- 8 hours to 5 days (commonly 48 hours) is the incubation window health departments cite for Pseudomonas folliculitis (“hot tub rash”), the itchy-bump infection linked to low chlorine and high pH — per Cleveland Clinic and state health-department guidance, it’s exactly the low-chlorine, high-pH combination this guide’s targets are built to prevent.
The 5 essentials at a glance
| Chemical | Job | Target level | How often |
|---|---|---|---|
| Sanitizer (chlorine or bromine) | Kills bacteria & germs | Cl 3–4 ppm / Br 4–6 ppm | Every 1–3 days |
| pH increaser / decreaser | Keeps water non-corrosive | pH 7.2–7.8 | As needed |
| Total alkalinity increaser | Stabilizes pH | 80–120 ppm | As needed |
| Shock (oxidizer) | Clears contaminants & smell | — | Weekly + after heavy use |
| Test strips | Tells you what to add | — | 2–3× per week |
According to the CDC, hot-tub water should hold a free chlorine level of at least 3 ppm (or bromine at least 4 ppm) and a pH of 7.2–7.8 to reliably kill the germs that cause hot-tub rash and respiratory illness — which is why a test strip, not guesswork, is your most important tool.
1. Sanitizer — the one non-negotiable
Sanitizer is what actually keeps the water safe. You have two mainstream choices, and you commit to one.
FROG @ease Floating Sanitizing System
- Drop-in floating cartridge — no daily measuring or granule dosing.
- Combines minerals with SmartChlor for low-effort, low-odor sanitizing.
- The manufacturer rates each cartridge to last up to 30 days and use up to 75% less chlorine than traditional dosing.
- Ideal for first-time Intex/SaluSpa owners who want "set and soak."
Long soaks are more relaxing with something to listen to — soak time is story time, so start a free Audible trial and get your first audiobook free.
For DIY control, chlorine (dichlor granules) from a brand like Leisure Time or SpaGuard is the cheapest and most flexible route — you sprinkle a measured dose, it dissolves in seconds, and you retest. Bromine tablets in a floating dispenser are the low-maintenance alternative: bromine stays effective across a wider pH range and holds up better in hot water, so it needs less babysitting, though it costs more and dissolves slowly. There’s a third path: a salt chlorine generator makes chlorine automatically from a little dissolved salt, cutting hands-on dosing to almost nothing — see our best salt water hot tub guide for the drop-in systems and salt-tolerant tubs worth pairing.
| Sanitizer | Best for | Pros | Cons |
|---|---|---|---|
| Chlorine (dichlor) | Budget & fast dosing | Cheap, dissolves instantly, easy to correct | Burns off fast in hot water; more testing |
| Bromine tablets | Low maintenance | Stable in heat, wide pH tolerance | Pricier, slow to dissolve |
| FROG @ease cartridge | Hands-off convenience | Floating, low odor, ~30-day cartridge | Higher cost per season |
Shop spa bromine tablets on Amazon →
2. pH increaser & decreaser
pH is how acidic or basic the water is. Below 7.2 it turns corrosive and stings your eyes; above 7.8 the sanitizer stops working and scale forms. A pair of Spa Up (pH increaser) and Spa Down (pH decreaser) lets you nudge it back into the 7.2–7.8 window.
Leisure Time Spa Up & Spa Down
- Spa Down (sodium bisulfate) lowers high pH; Spa Up (soda ash) raises low pH.
- Small doses go a long way in a 200–300 gallon inflatable tub.
- Keeping pH in range makes your sanitizer work harder for less product.
3. Total alkalinity increaser
Total alkalinity (TA) is pH’s shock absorber — it keeps pH from bouncing around every time you add chemicals. Target 80–120 ppm. If your pH won’t hold steady, low alkalinity is almost always why, so balance TA first on a fresh fill.
Shop alkalinity increaser on Amazon →
4. Shock (oxidizer)
Shock burns off the invisible gunk sanitizer leaves behind — sweat, oils, lotions — and clears that “used water” smell. A non-chlorine shock (MPS/potassium monopersulfate) lets you soak again in ~15 minutes; a dichlor shock doubles as a sanitizer boost. Shock weekly and after any party or heavy soak. For the full chlorine-vs-non-chlorine breakdown and dosing, see our best hot tub shock guide.
Leisure Time Renew Non-Chlorine Shock
- Oxidizes contaminants without spiking chlorine, so you can soak sooner.
- Keeps water clear and prevents cloudy, smelly buildup.
- Compatible with both chlorine and bromine systems.
5. Test strips — buy these first
You can’t dose what you can’t measure. A bottle of 4-in-1 or 7-in-1 strips tells you sanitizer, pH, alkalinity, and hardness in 15 seconds. AquaChek is the go-to. Test 2–3 times a week and always before adding anything. Strips are only about 85% accurate and stop being guaranteed past the expiration date printed on the bottle — for the brand-by-brand picks, the bromine-versus-chlorine strip difference, and when a liquid drop kit is worth owning, see our best hot tub test strips guide.
Shop AquaChek test strips on Amazon →
The shortcut: a spa startup kit
If picking each product individually feels like homework, a spa chemical startup kit bundles sanitizer, pH balancers, alkalinity, shock, and often test strips in one box sized for a small tub — the simplest way to get a new inflatable or plug-and-play spa running.
Spa Startup / Chemical Kit
- Bundles the five essentials at a lower cost than buying separately.
- Pre-portioned for inflatable-tub water volumes (200–350 gallons).
- Takes the guesswork out of your first fill.
The right order to add them
On a fresh fill, sequence matters:
- Total alkalinity first — it stabilizes everything after it.
- pH next, into the 7.2–7.8 range.
- Calcium hardness if your test strip shows soft water (scratchy on the skin, foamy water).
- Sanitizer last, once the water is balanced — adding it to unbalanced water wastes product and clouds the tub.
Always add chemicals with the pump running for circulation, and leave the cover off for about 20 minutes so gases can vent.
How much will chemicals cost?
Budget roughly $15–$40 a month for sanitizer, shock, and balancers on an average inflatable tub — less if you dose carefully, more if you soak daily or run a larger plug-and-play spa. It’s a recurring cost worth factoring into your total hot tub running cost. Because you rebuy filters and chemicals all season, it’s also worth checking whether Amazon Prime is worth it for hot tub shoppers before you stock up.
The bottom line
Hot-tub chemistry sounds intimidating but comes down to five products and a habit: test, then dose. Pick one sanitizer (bromine for low effort, chlorine for low cost), keep pH at 7.2–7.8 with balancers, shock weekly, and never dose blind — test strips first. For when to do each task — the weekly shock, filter rinses, and the drain-and-refill schedule — follow our hot tub maintenance guide. New to all this? Start with the tub itself: see our best inflatable hot tub roundup, the best plug-and-play spas, or the best two-person options. And once your chemistry is dialed in, round out your kit with the best hot tub accessories — spare filters, covers, and test strips included. Chemistry only works if the water is actually being filtered, so make sure you’re running the right cartridge: see our best hot tub filters guide for the part numbers that fit your spa.