In a 400 gallon hot tub, 17 mL (0.58 fl oz) of 8.25% unscented bleach raises free chlorine by 1 ppm. A typical after-soak dose from 1 to 4 ppm is 52 mL, about 3½ tbsp. With 6% bleach use 24 mL per ppm.
| Free chlorine | 8.25% bleach | 6% bleach | 10% liquid chlorine |
|---|---|---|---|
| Raise 1 ppm | 17 mL / 0.58 fl oz | 24 mL / 0.83 fl oz | 15 mL / 0.51 fl oz |
| Raise 2 ppm | 34 mL / 1.2 fl oz | 49 mL / 1.7 fl oz | 30 mL / 1 fl oz |
| Raise 3 ppm | 52 mL / 1.7 fl oz | 73 mL / 2.5 fl oz | 45 mL / 1.5 fl oz |
| Raise 4 ppm | 69 mL / 2.3 fl oz | 98 mL / 3.3 fl oz | 61 mL / 2 fl oz |
| Shock 3 → 12 ppm (CYA 30) | 155 mL / 5.2 fl oz | 220 mL / 7.4 fl oz | 136 mL / 4.6 fl oz |
Add
1.7fl oz
of Household bleach 8.25%
52 mL3½ tbsp
Raises free chlorine from 1 ppm to 4 ppm in 400 gal.
Check the product label. Strengths vary by brand, so enter the % printed on yours. Add one chemical at a time, into the water, and never mix chemicals.
Stabilizer is about 30 ppm now. Switch from dichlor to plain bleach so it stops climbing.
Save this test and get a reminder before your next soak.
Spa Calc for iPhoneComing soon to the App StoreUse plain, unscented bleach with no "splash-less" thickeners or added fragrance. Chemically it is the same as pool liquid chlorine, just weaker. A measuring cup or a cheap kitchen syringe kept only for the tub makes doses repeatable.
Bleach adds no stabilizer, which is why it is the second half of the dichlor-then-bleach method. It does raise pH briefly as you pour, so add it with the jets running and test pH separately. Never add bleach and pH decreaser together.
400 gallons is a typical 6 to 7 person acrylic tub. Doses are larger but the water is steadier; still test before every soak, and drain about every 67 days with two soakers a day.
About 17 mL of 8.25% bleach per 1 ppm. From 1 to 4 ppm: 52 mL.
Plain unscented bleach is sodium hypochlorite, the same chemical as pool chlorine. Dose it by the numbers, wait 15 minutes, and test before soaking. Soak when free chlorine is 3 to 5 ppm and at least 7.5% of your CYA (bromine 4 to 6) and pH is 7.2 to 7.8, at least 15 minutes after adding anything (20 after pH decreaser); after chlorine, bromine or a shock, test again first. Above 5 ppm chlorine or 6 ppm bromine, wait and retest in an hour or two; never soak above 10 ppm chlorine or 8 ppm bromine, or with pH below 7.0 or above 7.8. Below 3 ppm chlorine (4 bromine), add sanitizer first; at pH 7.0 to 7.2, raise pH first; with CYA above 40 ppm, drain and refill. Hot tub limits based on CDC guidance and EPA product labels.
No. Additives and thickeners cause foam and residue. Use plain bleach only.