Calculate exact chemical doses for your hot tub or spa. Chlorine, bromine, pH, and alkalinity calculator designed for small-volume spa water chemistry.
Select your hot tub volume using the presets (300–600 gallons) or enter a custom size. Choose what to calculate: sanitizer (chlorine or bromine), pH, or alkalinity.
Hot tubs typically use bromine instead of chlorine because bromine remains effective at higher temperatures (100–104°F). Ideal bromine: 3–5 ppm; ideal chlorine: 1–3 ppm.
Due to the small water volume, chemical changes happen quickly. Always add chemicals in small increments and retest after 15–30 minutes with the jets running.
A hot tub requires a sanitizer (bromine or chlorine), pH adjuster (pH up or pH down), and alkalinity adjuster (baking soda or muriatic acid). Bromine is preferred for hot tubs because it remains effective at high water temperatures (100-104°F / 38-40°C).
The ideal bromine level for a hot tub is 3-5 ppm. Bromine is preferred over chlorine in hot tubs because it stays active at higher temperatures and produces fewer odors. Test levels before each use.
Test and adjust your hot tub chemistry 2-3 times per week, or before each use. Due to the small water volume (300-600 gallons) and high temperatures, chemical levels can change rapidly. Always test before adding chemicals.
The ideal pH range for a hot tub is 7.2-7.6, the same as a swimming pool. Low pH causes skin and eye irritation and equipment corrosion. High pH reduces sanitizer effectiveness and can cause cloudy water.
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