How much bleach to put in a hot tub?
To raise chlorine from 1 to 4 ppm in a 400 gallon hot tub, add about 2.6 fl oz of plain, unscented 6% bleach.
How to work it out
- In short: work out how much chlorine the rise takes for your tub’s size, then how much of your product holds that much.
- 3 ppm × 1,514 L (400 gal) = 4.54 g of chlorine
- 4.54 g ÷ 60 g per litre (6%) = 76 ml = 2.6 fl oz
Household bleach is sodium hypochlorite — the same chemical as liquid pool chlorine — and many hot tub owners use it instead of granules because it adds no stabilizer. The catch is that a hot tub needs only a few fluid ounces, so measuring matters.
Adjust for your project
More options: Users
- To shock this tub
- 8.5 fl oz (1.1 cups) raises it about 10 ppm; then wait until free chlorine is back to 5 ppm or less before soaking (one EPA-registered chlorine label bars spa use above 5 ppm)
- Drain and refill about every (rule of thumb)
- 67 days
- The drain interval uses a common spa-trade rule of thumb — gallons ÷ 3 ÷ people using it per day = days between drains — not a standard. Your manual’s schedule comes first.
- Hot water and jets burn chlorine off fast. Test before each soak and keep at least 3 ppm (CDC).
6% bleach, 1 → 4 ppm, by tub size
| Tub | Add |
|---|---|
| 200 gal | 1.3 fl oz |
| 250 gal | 1.6 fl oz |
| 300 gal | 1.9 fl oz |
| 350 gal | 2.2 fl oz |
| 400 gal | 2.6 fl oz |
| 450 gal | 2.9 fl oz |
| 500 gal | 3.2 fl oz |
Bleach doses for a hot tub
At 6%, each 1 ppm in 400 gallons is about 0.85 fl oz (25 ml) — a little under two tablespoons. A typical top-up of 3 ppm is about 2.6 fl oz. Stronger 8.25% bleach takes about 1.9 fl oz for the same rise.
- Plain only. No scented, splash-less, gel or color-safe bleach — they contain other ingredients or less chlorine.
- Measure with a syringe or marked cup, kept for chlorine only, never for acid.
- Add with the jets on, cover open, and wait before soaking. The CDC minimum is 3 ppm.
- pH. Bleach is alkaline; small, frequent doses nudge pH up. Keep acid handy — see how much muriatic acid to lower pH in a hot tub.
- Freshness. Bleach weakens in storage, and a bottle in a hot garage weakens faster. If doses stop raising chlorine as expected, the bottle is the suspect.
Starting from fresh water? See how much chlorine to add to a hot tub on first use. The pool-sized version of this dose is on how much bleach for a 10,000 gallon pool.
Different size? Use the full Hot Tub Chemical Calculator (Chlorine, Bleach, Bromine).
What you’ll need
- Measuring pitcher (marked in oz and ml)Budget price
Measure doses instead of glugging from the jug. Keep one for acid and a separate one for chlorine.
See options on Amazon (opens in a new tab) - Hot tub test strips (chlorine or bromine)Budget price
Hot tubs move faster than pools; a strip before each soak tells you whether the sanitizer is still there.
See options on Amazon (opens in a new tab) - Liquid pool chlorine (sodium hypochlorite)Budget price
Adds chlorine without stabilizer or calcium. Strength is printed on the label — commonly 10% or 12.5% — and it weakens with age and heat, so buy it fresh.
See options on Amazon (opens in a new tab)
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Frequently asked questions
How much 8.25% bleach for a 400 gallon hot tub, 1 to 4 ppm?
About 1.9 fl oz.
How much bleach to shock a 400 gallon hot tub to 10 ppm?
About 7.7 fl oz of 6% bleach from 1 ppm.
How much bleach for a 250 gallon inflatable hot tub, 1 to 4 ppm?
About 1.6 fl oz of 6% bleach.
Other common sizes
- How much chlorine to add to a hot tub on first use — 1.6 fl oz
- How much bromine to start a hot tub — 6.4 fl oz of bromide booster
Sources
- CDC Healthy Swimming — Staying healthy in hot tubs (opens in a new tab) — No hotter than 104°F (40°C); chlorine at least 3 ppm, bromine 4–8 ppm, pH 7.0–7.8; no children under 5.
- CDC Healthy Swimming — Home pool and hot tub water treatment and testing (opens in a new tab) — pH 7.0–7.8; free chlorine at least 1 ppm in pools (2 ppm with cyanuric acid) and 3 ppm in hot tubs; no CYA in hot tubs; test twice a day.
- CDC Healthy Swimming — Operating public pools, hot tubs and splash pads (opens in a new tab) — Hot tubs: at least 3 ppm free chlorine or 4 ppm bromine; water no hotter than 104°F (40°C).
- CDC — Model Aquatic Health Code, 5th edition (2024), code (opens in a new tab) — Free chlorine minimum 1.0 ppm (2.0 with CYA, 3.0 in spas); pH 7.0–7.8; CYA at or below 90 ppm; CYA:FC above 45:1 is an imminent hazard; TA 60–180 ppm; turnover tables.
- Leisure Time — Spa 56 chlorinating granules (dichlor) label (opens in a new tab) — 99% sodium dichlor dihydrate, 55% available chlorine; ½ oz per 500 gallons for a 2–3 ppm residual; 1 oz per 500 gallons to shock.
- Leslie’s — Chlor Brite spa shock (dichlor) label (opens in a new tab) — Half an ounce per 500 gallons; 1.5 oz per 500 gallons after use.
- Leisure Time — Reserve (sodium bromide) label (opens in a new tab) — Sodium bromide 32.18%; 4 oz per 250 gallons at start-up; 1 oz per 250 gallons weekly.
- Leslie’s — Bromine Tabs Plus label (opens in a new tab) — 98% active ingredient; 3 tablets per 300 gallons in a floater or feeder.
- SpaGuard — Brominating Tabs (opens in a new tab) — BCDMH 98%; target active bromine 3–6 ppm.
- OxyChem — Soda Bleach Solutions Handbook (re-hosted copy) (opens in a new tab) — Trade percent = grams per litre of available chlorine ÷ 10; weight % NaOCl ≈ 1.05 × weight % available chlorine; strength and specific gravity table.
- US EPA reg. 42177-80 — sodium dichlor label (ProPools copy) (opens in a new tab) — Dihydrate, 56% available chlorine; 2–3 oz per 10,000 gallons daily; 1 lb per 10,000 gallons to superchlorinate.
- CDC — Pool chemical injuries press release (2014) (opens in a new tab) — Never mix pool chemicals, especially chlorine products with acid; add chemical to water, never water to chemical.
- CDC — Pool chemical safety: storage poster (opens in a new tab) — Separate acid and chlorine; don’t mix different types of chlorine; keep chemicals cool, dry and in original containers.