In a 500 gallon hot tub, 3.4 g of 56% dichlor granules raises free chlorine by 1 ppm. Going from 1 to 4 ppm after a soak takes 10 g (0.36 oz, about 2¼ tsp). Weigh it on a kitchen scale if you can: scoops vary.
| Free chlorine | Grams | Ounces | Approx. measure | CYA added |
|---|---|---|---|---|
| Raise 1 ppm | 3.4 g | 0.12 oz | ¾ tsp | +0.9 ppm |
| Raise 2 ppm | 6.8 g | 0.24 oz | 1½ tsp | +1.8 ppm |
| Raise 3 ppm | 10 g | 0.36 oz | 2¼ tsp | +2.7 ppm |
| Raise 4 ppm | 14 g | 0.48 oz | 1 tbsp | +3.6 ppm |
| Shock 3 → 10 ppm (CYA 20) | 24 g | 0.83 oz | 1¾ tbsp | +6.4 ppm |
Add
0.36oz
of Dichlor granules 56%
10 gabout 2¼ tsp by volume
Raises free chlorine from 1 ppm to 4 ppm in 500 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.
Use dichlor for the first week or two until stabilizer reaches about 30 ppm.
Save this test and get a reminder before your next soak.
Spa Calc for iPhoneComing soon to the App StoreEvery 1 ppm of chlorine from dichlor also adds about 0.9 ppm of cyanuric acid. That is useful at first: stabilizer around 30 ppm protects chlorine in a hot tub. After roughly 33 ppm of chlorine’s worth of dichlor, switch to plain bleach so CYA stops climbing. That is the dichlor-then-bleach method.
Sprinkle dichlor into the water with the jets running and the cover open, and wait at least 15 minutes before soaking. Keep the container dry and closed; never mix it with other chemicals.
500 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 83 days with two soakers a day.
3.4 g of 56% dichlor per 1 ppm. From 1 to 4 ppm: 10 g.
Wait at least 15 minutes with the jets running, then test. 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.
Dichlor adds stabilizer (CYA) every time. Once CYA reaches about 30 ppm, bleach keeps chlorine up without adding more.