In a 300 gallon hot tub, 13 mL (0.44 fl oz) of 8.25% unscented bleach raises free chlorine by 1 ppm. A typical after-soak dose from 1 to 4 ppm is 39 mL, about 2½ tbsp. With 6% bleach use 18 mL per ppm.
| Free chlorine | 8.25% bleach | 6% bleach | 10% liquid chlorine |
|---|---|---|---|
| Raise 1 ppm | 13 mL / 0.44 fl oz | 18 mL / 0.62 fl oz | 11 mL / 0.38 fl oz |
| Raise 2 ppm | 26 mL / 0.87 fl oz | 37 mL / 1.2 fl oz | 23 mL / 0.77 fl oz |
| Raise 3 ppm | 39 mL / 1.3 fl oz | 55 mL / 1.9 fl oz | 34 mL / 1.2 fl oz |
| Raise 4 ppm | 52 mL / 1.7 fl oz | 73 mL / 2.5 fl oz | 45 mL / 1.5 fl oz |
| Shock 3 → 12 ppm (CYA 30) | 116 mL / 3.9 fl oz | 165 mL / 5.6 fl oz | 102 mL / 3.5 fl oz |
Add
1.3fl oz
of Household bleach 8.25%
39 mL2½ tbsp
Raises free chlorine from 1 ppm to 4 ppm in 300 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.
Inflatable tubs near this size include the Intex PureSpa Bubble Massage 85" round (6 person) (290 gal) and the Intex PureSpa Jet & Bubble Deluxe 86" square (6 person) (290 gal). 300 gallons is a common 4 to 6 person size. Two people soaking for 20 minutes typically use 1 to 3 ppm of chlorine; your log will show your own number after a couple of weeks.
About 13 mL of 8.25% bleach per 1 ppm. From 1 to 4 ppm: 39 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.