Hot tub dosing chart
The common hot tub chemical doses, in ounces by weight, for spa sizes from 200 to 500 gallons. These are the same numbers the dosing calculator computes, laid out as a plain chart: find your spa's volume, read across. If you don't know your gallons, the volume calculator gets you there in a minute.
| Adjustment (product) | Per 100 gal | 200 gal | 250 gal | 300 gal | 350 gal | 400 gal | 450 gal | 500 gal |
|---|---|---|---|---|---|---|---|---|
| Raise total alkalinity +10 ppm sodium bicarbonate | 0.24 oz | 0.48 oz | 0.60 oz | 0.72 oz | 0.84 oz | 0.96 oz | 1.08 oz | 1.20 oz |
| Raise free chlorine +3 ppm dichlor granules | 0.07 oz | 0.14 oz | 0.18 oz | 0.22 oz | 0.25 oz | 0.29 oz | 0.32 oz | 0.36 oz |
| Raise bromine +3 ppm bromine granules | 0.07 oz | 0.13 oz | 0.17 oz | 0.20 oz | 0.23 oz | 0.26 oz | 0.30 oz | 0.33 oz |
| Lower pH 7.8 to 7.5 sodium bisulfate | 0.75 oz | 1.50 oz | 1.88 oz | 2.25 oz | 2.63 oz | 3 oz | 3.38 oz | 3.75 oz |
| Chlorine shock (+10 ppm) dichlor | 0.24 oz | 0.48 oz | 0.60 oz | 0.71 oz | 0.83 oz | 0.95 oz | 1.07 oz | 1.19 oz |
| Non-chlorine shock (routine) potassium monopersulfate | 0.40 oz | 0.80 oz | 1 oz | 1.20 oz | 1.40 oz | 1.60 oz | 1.80 oz | 2 oz |
Ounces are by weight, not volume; a kitchen scale beats a scoop. For spoon equivalents and doses tuned to your exact test readings, use the interactive calculator, which converts each product to teaspoons and tablespoons.
Target water ranges
| Parameter | Range | Ideal |
|---|---|---|
| pH | 7.2–7.8 | 7.5 |
| Total alkalinity | 80–120 ppm | 100 ppm |
| Free chlorine | 3–5 ppm | 4 ppm |
| Bromine | 4–6 ppm | 5 ppm |
| Calcium hardness | 150–250 ppm | 200 ppm |
Add one chemical at a time with the pump running, wait at least 30 minutes, and retest before adding more. Never mix chemicals directly with each other, and follow the label on your specific product: concentrations vary by brand.
Common questions
How much chlorine do I add per 100 gallons?
About 0.07 oz of dichlor granules per 100 gallons raises free chlorine about 3 ppm. For a typical 300-gallon hot tub that is roughly 0.21 oz, about a heaping teaspoon. Test first and dose to your actual reading.
Where do these numbers come from?
They are computed from published water-chemistry dosage rates (Taylor Technologies and PoolMath dosage tables, product available-halogen fractions, and PHTA range guidance), generated at build time by the same math that runs the dosing calculator, and checked by automated assertions. The sources are listed below the chart.
Why is my product label different?
Concentrations differ by brand, and pH adjustment in particular depends on your water’s buffering, so label increments vary. Treat this chart as the standard starting dose for generic products, add in small steps, and let your test kit have the final word.
Sources and method
- Sodium bicarbonate raises total alkalinity about 10 ppm per 1.5 lb in 10,000 gallons (standard pool/spa dosage tables; Taylor Technologies; Trouble Free Pool PoolMath).
- Dichlor (sodium dichloro-s-triazinetrione dihydrate) is about 56 percent available chlorine; dosing is by available-halogen content (1 mg/L product per 1 mg/L residual, divided by the available fraction).
- Bromine granules / BCDMH are about 60 percent available bromine; spa bromine is carried at 4 to 6 ppm.
- Balanced-water ranges follow common spa water-care guidance (PHTA/APSP ranges and typical spa product labels): pH 7.2 to 7.8, total alkalinity 80 to 120 ppm, free chlorine 3 to 5 ppm, bromine 4 to 6 ppm.
- pH adjuster rates are representative spa-label increments and are buffer-dependent estimates; always add in small steps and retest.
Chart generated 2026-07-27 from the site's dosing dataset. The full dataset is available as plain JSON. See about & method for how the numbers are computed.
Related
- Chemical dosing calculator (exact doses from your test readings)
- How to shock a hot tub
- How to lower pH and raise pH
- How to raise alkalinity